Ok, replaced the rears (on the wear strip) with Hawk Ceramic and Brembo Rotors (didn't want to worry about those crappy stock rotors)...and just realized that I forgot to remove the shims from the old pads and put them on the new pads, a week ago.

The old pads/shims are gone...how bad have I screwed this up? Can I buy replacement shims?

 

You'll be fine. You may hear brake squeal later down the road, but nothing really seriously wrong without the shims. I didn't run shims in my Prelude. If you're still worried, just buy some replacement shims from the dealer.

 

I did that with the front rotors and my ebc redstuff pads a year or two ago. All the dealers I've checked said the shims themselves are about the same price as you would pay with stock pads that include the shims ~$55.

 

Kinda figured that...I was just concerned the pads might ge damaged with the caliper pressing directly. If that's the case, I'll just run without...

 

Nah, you should be alright. I ran pads without shims for years on my last 2 cars. Without the shims you will hear them squeal a lot sooner than you would otherwise, but its just an annoyance.