I don't know if the outer dimensions are enough of a difference to allow it to go across the platform. I have a 40 cal Gen 1, and I'd hate to sell it to you to find out its not a fit. I am a fan of either Alien Gear or Dara. Reasonable prices and great stuff. Both Yankee made, last I checked. Alien Gear sometimes has a deal of BOGO on certain styles. That is what I did.
Yeah, check those sites out. Or google "The Holster Store" online. Really affordable, their stuff I have used before. Takes a beating and keeps on holding. If you have a way to take the edge off the steel clip, file or emery paper, you'll save your shirts from all having a tear in them right where the clip is. =-p
I have a Bianchi Professional 100 IWB holster size 11 for my PPS40. IIRC, the PPS 9mm Classic uses a size 10-A. My daughter has a PPS Classic 9mm and carries hers in a Kusiak Leather IWB holster like the one featured here as an Old Fashion IWB... Kusiak Leather - Conceal Carry Holsters - Minimalist Leather Holster. I must confess, I liked her choice a lot.
According to Wikipedia, the Classic 9mm and .40 have the same measurements. Barrel: 81mm 3.2"; Length: 160.5mm 6.32"; Width: 27mm 1.1"; Height: 112mm 4.4" with small mag. Mass is different... 9mm 550gr 19.4oz vs .40 560gr 19.8oz.