I'm assuming you're talking .357 mag. Which barrel length; 2.25" or 3.06"? I ask because there's a lot more available for the 2.25" ( I know because I have a new 3.06" & haven't found what I'm looking for yet!).
You may already know...the SP101 shares the same cylinder dimensions (for speedloaders, etc.) with the S&W J-frame. Most of the J-frame holsters will work with the 2.25" barrel (unless they're VERY CLOSELY molded or fitted). So it's best to trial fit or ask the manufacturer. Also, check-in with "Gemini Customs, LLC" as they're a top SP101 custom shop. They know these guns & the associated suppliers as well as anybody. Sometimes they have "tough to find" holsters in-stock. Enjoy your 101.