Many of us have been told by reloading suppliers that it is illegal to export reloading supplies including wads and hulls from the UK. Neil please comment about this.

CL -
from experience that statement is false. And from enquiries here in UK the source of that is perhaps misleading - if not actually disingenuous.
But it is not for me to sway your opinion.

Milton, you may try " jug choking " your gun. .010 choke is only .005 on a side. An adjustable reamer and a slotted 1/2" aluminum about 3' long to adjust the reamer while in the barrel is all that's needed. The reamer will cost you a bit over a Franklin, but then you'd have it.

My view on "adding " choke - I would only consider it in a really thick walled barrel, preferably a single. Removing metal is rather a one-way street.
If the bore diameter is .835"+ and there is no/minimal choke I would just use a plastic wad, wrapper and buffer....( lead shot)...but may well work with bismuth.

I have seen some really good patterns out of muzzleloading shotguns that have been jugged choked, another method ive read about that doesnt remove metal is having fixed choke sleeves soldered in.