Boy, I'm gonna have fun with this. The 345 is not even listed on Ruger's chart on that site. Well, there's no fire. I'll find something.
If you live near a large sporting good store (Like a Cabelas or a gun-specialty store like Mackeys in NC) they will usually let you bring your (unloaded) firearm in and "test fit" holsters...
NOBODY lists a leather holster for the Walther P22. The only "official fits" for it are those Fobus monstrosities. I wanted a nice tan leather paddle for range use when I took my daughter to the range (she is very style-conscious...).
After searching the Net, I found several references to the Walther fitting holsters for sub-compact Glocks, so I went to Mackeys (which has a HUGE selection of leather--Galco, Bianchi, Safariland) and tried a few Bianchi's and finaly found one--for a Glock--that fit like it was made custom for the Walther...
So you never know when it comes to fitting a holster. Many firearms are similar enough in dimensions that they are essentially interchangeable. Leather is also more likely to give you an "alternate fit" than kydex or nylon because it gives and will "learn" to fit the new pistol after a few days...
This just gives you an excuse to spend an hour or so browsing in a gun store--searching for the "perfect holster" using hands-on shopping techniques. What's not to like? I can think of few other activities that would be a better way to spend an afternoon...
Good luck.