I would NOT try to shrink a K-frame holster, as much as I like the Bianchi models mentioned above. I wore a 5BHL in black basketweave stamping for over 20 years, and like it very much. (The gun is a M-66-3.)
I think you need to skip a few movies or something and save for a custom rig, probably from El Paso Saddlery.
www.epsaddlery.com
Look at their historical holsters and at the Tom Threepersons and 1930 Austin models. Their basketweave stamping & floral carving are superb. I own several of their holsters, two for the M-60-4. You'd probably want longer versions of those holsters. One is like the old Safariland M-29; the other, a Threepersons.
But first, shoot that gun some and see if it extracts empty brass and is accurate. I had a miserable experience with a S&W M-34. Had to POUND out the fired brass. I'll never again buy an S&W .22 revolver!
What have you got, a Model 35? If it works well, treasure it and be happy with it. That's a good way to get six-inch bbl. velocity in a gun light enough for handy carry. If you don't have my extraction difficulty, that gun is worth a good holster.
I SERIOUSLY doubt that you'll find a used J-frame holster for a six-inch barrel. I had to order both of my El Paso holsters for the M-60-4. I also doubt that Bianchi will do any custom work today. I asked them for holsters for my M-60-4 and was told to try to cram it into their usual three-inch 5BHL! Of course, the full-lug barrel made that impossible. I was NOT impressed with their rep's attitude!
Finally , post in The Lounge for Lobo Leather to contact you. Judging from photos, he does really nice work and he's a member. He may be able to beat El Paso's prices.