I think the answer lies in these four questions:
1. Each year, how many hunters and/or target shooters decide to become a "vintage style" double gun shooter for the first time?
2. Each year, how many current double gun owners decide to add another "vintage style" double gun to their safe without selling/trading one in exchange?
3. Each year, how many vintage double guns actually become unusable and are retired?
4. Each year, how many new "vintage style" double guns are made?
I don't know the numbers, but the current double gun market run has been going on for about 30 years, and I would guess that supply has more than caught up with demand - pricing certainly would indicate that.
I think the issue is particularly tough for the Spanish makers, because target shooting is the one area that continues to grow, at least according to the NSSF, and they do not sell target guns in the US. As has been alluded to by others, hunting upland birds with light sxs is not a growing market segment.
Of all of the hunters and shooters I know, I would estimate that maybe 20% have any interest in owning or shooting a "vintage style" double gun. The guys I hunt with the most think a Beretta OU is more than adequate for their needs - and their choice is not limited by their pocketbooks. They would would characterize it as picking an Acura over a Alfa Romeo.
Sidelock OUs for target or hunting might be an area worth exploring - other than CSMC A10s, there are no options available for less than $25k new. But they would have to be based on the Woodward/Boss designs, and not the Merkel double under lump that AyA has used in the past.
And since you asked, my only experience ordering a custom mid-range Spanish sxs sidelock ended badly, as the gun was not well made. Fortunately, the importer agreed to take it back, but that was after a long wait for the gun (including several missed deadlines that had been agreed upon in advance) and a fair amount of kibitzing to get things worked out. The importer probably should not have sent it to me, but the maker should not have shipped the gun in the first place.
