I have imported guns from Germany, Italy, UK, and Switzerland. Now the UK is virtually impossible - Germany is a snap.
UK there is only 1 company that will export anything that can be considered a firearm - that would be a pipe with a small hole in it. You cannot disassemble them and ship in pieces or anything - age does not matter. You will wait for 3 - 6 months or more. You also HAVE TO HAVE a US customs broker you pay to handle getting it in the United States. If you try to handle that customs paperwork yourself - you might as well just forget it.
Whatever you win the auction for - add 50% to 60% before shipping - that usually is a 25% - 30% buyer premium plus, 20% VAT Tax, plus you WILL pay customs US state taxes, and then of course all the little fees they tack on here and there for handling.
So Expect 1 year - a $#*! of a part time job - and misery plus adding about 60 - 75% money on plus your time. If there is a spec of Ivory or animal material on it - add another 6 months and 3 inches of paperwork for CITES permits.
Just watch the auctions and enjoy the beauty - you will never get them here. I've been down every avenue and the best I could come up with was pre COVID and that was workign with a Shotgun reseller/vendor here in US that ships 2 times a year in bulk - these are 10K English shotguns. I could pay him and piggyback on his shipment. But you have to pay to get someone to go pick it up and pack it and deliver it to the actual shipper. Since its a firearm - no pack and ship or packing pick up will touch it.
Thomas Del Mar was the last buy - 1730 French Pistol - I got it - took $#*! and lost most of my hair - but in the end it was more than I will ever get for it.
Good luck should you try!!!
You can work with Hermann Historica and Czerzys - but expect about 3 - 6 months to get here and shipping is a fortune. Last over under Miquelet late 1700's gun from Italy I Paid 950 pack and ship - took 5 months. Beautiful gun - but again - not a bargain.