Ruger GP100 6" .357 leather holsters...
Depending on a few basic factors; color, belt width(1.5-2.25"), cant, designs, etc I'd check these websites/sources;
Tex Shoemaker, Don Hume, DeSantis, the Bianchi Cyclone 111 rig, The Sportsmans Guide, Galco.
For a shoulder rig I'd check into a Lawman Leather Goods STU or a brown leather Dirty Harry;
www.Lawmanleathergoods.com .
I looked into buying a 6" blue steel GP100 revolver(with state mandated .38spl rounds) and packing it on a few armed security details for Ss & Gs
, but haven't had the time or $$$ yet.
I'd use a 2.25" width black nylon holster(left hand) with it.
I'd want to annoy the local cops & look like the Texas Ranger Captain in the action classic LoneWolf McQuade(1983)
www.imfdb.org
"Style. The great ones always had style."