"have turned up at this dealer, and apparently the seller is taking them to a couple in the district to gain the best price."
You have viewed the guns at the dealers place of business.
"I do, never the less, have a good working relationship with him, and he looks after me."
You have the opportunity to make all parties happy.
Discuss with your dealer friend your proposal i.e. :"about the fairly complex, arcane, and specialised world of vintage English guns"
Make an offer to the dealer re some compensation for his good fortune and inquire as to the possibility of direct negotiations with the principal, who in short order will have at least 3 offers of fair value to consider. If direct contact is not available to you then deal with/through the shopkeeper.
Deals come and go.
Friendships are valued in lifetimes.
Good Luck.
