Chapuis RP roundbodies can be ordered in 28 gauge, and would be in the $8k price range including upcharges for subgauge, SNST and PG. William Larkin Moore has info about them on their website Chapuis

Further off the beaten path, and likely over $8k:
SIACE (more reliable Italian SSTs, but monoblock barrels if that matters)
Verney Carron MBAG
Verney Carron Kebco


Such a long, long time to be gone, and a short time to be there.