I feel your pain, brother.
Since the SW99 and P99 are brand new, not many holsters are made for them. I did find (and purchase) two, though: one leather pancake type and one IWB.
Lucky for you, I have my Walther in the IWB in my deskdrawer! I'll check it out for you.
It's an Uncle Mike's Sidekick Size 15. It's about 15 bucks, and I highly recommend it. It's thin, and is very easy to put on and take off. It works with my Sig 229, as well.