Old Faithful Holsters sells a hybrid IWB holster specifically for the P-01.
I ordered one on 3/9 and received it yesterday (20 days later). I've worn it less than 24 hours, but so far, it is comfortable and should break in even better. I'm pretty sure some of the other hybrid holster makers do the P-01 as well, such as Crossbreed Holsters and Theis Holsters.