The differences between S&W .38 Special J-frames and .357 Magnum J-frames are minimal, basically slight differences in cylinder length and diameter, or in a few cases, frame length. Holsters that fit the former will generally fit the latter, and vice versa, for a given barrel length.
"...sp101, the j frame, and taurus small frame all use the same holsters..."
Unfortunately, this is NOT true.
Many S&W J-frame holsters will fit the small frame Taurus guns like the Model 85. After all, all of Taurus' original tooling was what Bangor Punta left there in Brazil when S&W changed ownership, and their original revolver designs were close copies of the Smiths.
OTOH, holsters made for J-frames WILL NOT fit the Ruger SP101. I have half a dozen J-frames and two SP101s, and all the J-frames fit in the same holsters as each other, but the SP101s won't fit in any of these. It's simply a bigger frame size.