You can order shims from Pentax(directly).
I usually grab the entire batch(8-10 of them) when I pick-up a new body.
Though I'm still on the fence with the K-5 given it's advanced LV capabilities.
Either way, screen shimming is always a bit of a chore.
And your experience is a great reminder of the implications that come with them.
However, if its of any help, you can wash your screens back to a pristine condition by washing them in baths made-up of mild dish soap distilled water. I usually set-up a few foam cups(1 x wash and 2 rinse) with distilled water. After which I dry the screen off with a blow-drier(careful not to blow it away!) and dabbing the drops off onto a tissue(for absorption).
Also, I would advise never to handle your screens with bare hands. Even though the installation tweeters are essential to installing/removing the screen, it is far better to have full contact access to the mirror box and such without worrying about the effects of oils and dust from your hands.
Oh. and I don't know if this applies to you or not, but do remember that screens can or will affect your metering at some stage. So I guess it end-up being a commitment of sorts for those who chose to use them. My own resolve, was to commit a body to MF and install and use a Katzeye with it exclusively(called it our manual).
Hope this helps.
PS. you can micro-calibrate a shim(
) with 3m tab tape which is very thin and easy to work with.