where is a good source if any for high capacity pistol magazines for the Ruger P95?

Yes, the P89 mags will fit in the P95.

Try www.cdnn.com, they had 15 round Mec-Gars the last I saw.  Probably the most reliable mag other than the Factory mags.

I have used a Pro-Mag Hi-Cap in the P95 I had and it worked very well, although it also fit the P85(mabe others?).
I'd sell it to you for $8.00+ shipping if I can find it. Its's in very good cond.
I probally ran 400-500 rounds(hardball) through it with only ONE FTF(it wasn't the fault of the mag).
The P95 pistols are very reliable in 1500-1600 rounds I only had ONE failure to go into battery completely(about1/4")and that was because of lack of enough lube after about 400 rnds of shooting.