EU REACH regulations made the import of a considerable number of powders illegal some two (or was it three?) years ago. This included the entire Thales / ADI produced range of 'Extreme' extruded powders marketed under the Hodgdon label (plus IMR-8208 XBR which is same source / family), older St Marks ball grades such as W748/760 and H380 / H. B-L(C2). We also lost all older Du Pont era IMR grades such as 3031 and 4064. but not the modern CFEs, StaBALL 6.5, Alliant Power-Pro range.
All European manufactured powders are REACH-compliant, so that's Lovex (Shooters World in the US), Norma, Reload Swiss, and Vihtavuori marques, but also all Alliant Reloder grades (made in Sweden and Switzerland) and Ramshot ball powders (Belgian). In addition, the six new Canadian IMR 'Enduron' powders are REACH-compliant, so we've retained those.
The REACH issue is about a tiny part of the banned powders, less than 1 or 2% content of various older burn rate and similar chemical 'modifiers'. The real risk to health and the environment is nil! I'm sure nevertheless that the US will sooner or later go the same way. It is said that ADI is currently developing modified 'green' and 'safe' versions of its range in response.
So far as the effect on US H. VarGet, H4350 etc consumers go, REACH has been beneficial in that a major alternative market has been cut out and supplies now remain within the American continent(s) once landed and shipped to Hodgdon.
As I understand it, Thales / ADI is making as much of the Extreme range as can be shipped. That is the primary bottleneck. Powders are shipped in bulk from Sidney to somewhere on the US West Coast, and there is a single shipping company serving the route with limited capacity. Moreover, it serves New Zealand en route and the port concerned has explosives weights limits on one of its two piers. So, many ships' captains refuse any shipment weight above the lower level to avoid potential delays in docking. On top of that there is the post-Covid shipping crisis which no doubt doesn't help either if the ships are stuck in queues waiting to dock at either end.
This sets the ceiling on US imports of these powders. The only other possible supply-end factor is whether 'local' demand has risen, 'local' as in Australia and New Zealand where they're sold under the ADI brand name and ADI's own product descriptions - at very high prices if forum complaints by shooters in those countries are believed - no discount for local users at all! Australia has always been security conscious and was ramping up its military preparedness even before the Ukraine invasion in response to the growing Chinese threat, so military demand met by ADI's ammunition manufacturing division may have increased taking up additional powder too.
Nevertheless, the overwhelming majority of these powders end up in Kansas. So the grade breakdown is largely in Hodgdon's hands. Last year and that before, all you US-based guys on this and other forums were screaming 'We want H4350!'; 'More H4350!', and now you've apparently got it. (Or, maybe that's just a perception of availability vis a vis VarGet as personal experiences at the LGS counter aren't exactly reliable indicators of the overall situation.)
I've been doing an analysis (and range testing) of alternatives to the 'Fab Four' (H4895, H4350, H4831 and H. VarGet) post-REACH, and the simple answer is substitution. There are plenty of alternatives - around 15 each for H4350 and H4831 of which two or three are Europe-only powders, and no fewer than 27 for the H4895/VarGet pair, again with two or three 'local' powders. (But you actually still have a much, much wider choice as you have all the other REACH-affected powders which we've lost as well as some grades that don't get here primarily 'accurate' labels.) There are a few cartridges where these ADI powders really are ideally matched, eg VarGet and the 6mm Dasher, but most applications have just as good alternatives. (I grind my teeth to see threads or posts on this forum with people quoting VarGet loads in common or garden short-distance non-precision 308 Win loads - what a waste to burn VarGet in this most powder-flexible of cartridges for all than a handful of specialist loads!)
Of course, saying there are alternatives may not help if those grades aren't available in the LGS either and that's a result more of the growing imbalance between supply and demand for these products across the West for which there is no short-term structural 'fix', and things may in fact get [much] worse as 1) there seems no end to the US public 'tooling up' and wanting factory ammo for its new guns, and 2) the end - and in fact partial reversal - of the post USSR implosion / end of the Cold War Peace Dividend (which was severely overdone by many countries which in effect demilitarised completely and if they have any sense will have to start military spending again in a big way!)
Countering that, I suspect though that in the short-term at least, demand will reduce and shortages ease or even abate entirely - we in the West are all facing a lot of economic and personal financial pain with looming recessions and out of control price inflation. Most factory ammo and handloading supplies demand is highly discretionary, and as people become poorer or lose their jobs, civilian demand will reduce. Not nice, but it'll put supply and demand back into balance.
We in Europe learned to forget the more popular Hodgdon powders long, long before REACH, for the simple reason that supply became so irregular and inadequate. Most of us don't miss them. H4831sc for F-Open shooters using 284 and the short magnums is probably the most missed now as it really fits a niche.