There is not much of an after market for the PPS. Fortunately it does not need much upgrading.
I have OEM night sights on mine. Got them several years ago when the only source was Earl's. I also use a TLR-3 light on the gun when I am out of town as the PPS is not my night stand gun when I am at home. I might also add I have a Hogue grip sleeve. It add's a little bit of a palm swell, that I like.