If you guys in Britain would just hold periodic weekend events, suppliers like Steve and Digger could show up and hand you these unshippable chemicals. That's how I generally get materials like barium chlorate, realgar, Paris Green, black powder, etc without having to pay twice what they cost for shipping.
This is what the rocket guys do.
I can arrive at a meet and have pre ordered supplies arrive at site via a mobile shop
With sufficient planning i do not even need to take any ADR goods away afterwards.
Thing is there is a legal framework for this in place.
There is no equivalent for pyro in the uk.
Any meet would be restricted to firing purchaced fireworks with UN numbers.
As exat has pointed out there is the added problem of private carriage of hazardous goods.
I know it happens, methanol for biodiesel is a fairly common one.