You can check with Ruger directly for wood grips. They sell some for their other handguns on their webpage.
If you don't find them there, you can check with Dixie Gun Works for both grips and holsters.
Dixie's leather goods have given me great service for all my cap 'n ball and Civil War reenacting goodies. They are not too terribly expensive, and worth the coin.
They offer several models just for the Old Army, and some general "large frame" leather that will fit, including flap holsters.
www.dixiegunworks.com