Hello Bill,
Good luck with your search...here is another site ,I think these guys might have a bigger selection ]Blackbern guns[/url]
http://757arms.com/.Whats your plan...cast round ball or cast slugs?.or factory slugs or sabots?.
Are you going to regulate the bbls yourself?, as you prolly know, the chances of both bbls putting two big holes close together without some regulation tinkering are not that great.
I have been looking for a nice heavy English single to sleeve with a rifled bbl, to avoid the regulation issue.
Please keep us posted as to what you end up with & how it shoots...I for one am interested...good luck with the project Oregon Bill
cheers
Franc