I too had been looking for a holster for a large frame revolver - my .500 Smith & Wesson Bone Collector.
I finally gave up but ran into a Mark Finnegan of Shamrock Holsters at the Great American Outdoor Show in Harrisburg this past February.
He claimed he could make a holster for my revolver so I took a chance and had him make one for me.
I am happy to say I just received it and I am very pleased.
The leather is thick, soft & supple and fits my scoped Bone Collector like a glove.
I ordered the accessory cartridge bandoleer.
The holster also has holes at the muzzle end for a strap that you could tie to a leg if you wanted to.
I'm still getting used to it but it is a simple, fine, sturdy piece of work.
The holster system is an interesting modular one so the belt I ordered could probably be used with another holster-gun combination.
REF:
https://www.shamrockholsters.com//
EDIT: the "belt" I ordered is actually a shoulder belt and not a waist belt. It's quite comfortable. Shamrock calls it the "Bandito Shoulder Belt",