I appreciate the heads up as I have a rather unique William Ford 3.25" 10 gauge that uses Heath's chamberless patent (10 gauge chambers and 8 gauge bores, so no forcing cone to speak of.)

Simpson's didn't list 8/10s, but did have two lots of 10/12 shells, one of which is: http://www.simpsonltd.com/product_info.php?products_id=47803

Since my Ford's barrels were designed for thin walled brass shells, so they could use the largest possible wads, I haven't tried to get lathe turned shells made, since these are typically thicker walled.