I breezed through the thread pretty quickly, so I apologize if someone already posted this info. Of the 3 "decent" holsters I have, this is what I've found:
1) My old (like 10-15yrs old) Blade-Tech IWB for a G19 will not fit at all (way too small for the gun).
2) My Comp-Tac MTAC for my G19 just barely fits, but it's really tight - far more than I'd like or be comfortable with.
3) My Comp-Tac MTAC for my G30, with the retention screws tightened down, fits great (nearly perfect).
If I end up up using my P-10C as my EDC gun, I definitely plan to use the G30 MTAC, instead of spending extra money on a holster that's designed specifically for the P-10C.
9/5/17 - Edited to Add: I know it's been decent amount of time since this thread started (and the P-10C has been out), so I guess it's not surprising that more and more holster makers are making P-10C specific holster. Just as an example, I just took a look at Comp-Tac's site, and most of their holsters are now available for the P10C, including the MTAC's replacement "spare bodies", which is a nice option if you already have a current generation MTAC that you want to convert ($25 for the replacement body vs. $81 for a whole new MTAC).