Get one of those army officer's button flap holsters that they used to
keep their long barreled Colts and Remingtons in, the ones they wore
in the War of Northern Aggression, aka US Civil War...they'll work!
Spock here, Captain...logically, Cabelas USA has everything...so I did a long range sensor scan of Cabelas.com, and came up with item IK-227087, designed to fit the Smith & Wesson 500 with 8 3/8" barrel, for $65. You'd have to find out if your revolver is similar to the Smith, but there you are Captain! Hope it works for you!
Go Custom or use a long holster with an open bottom if you don't mind the muzzle being exposed.