Just bought like 6 of these on Amazon:
http://www.amazon.com/mn/search/ref=sr_nr_scat_705324011_ln?rh=n%3A705324011%2Ck%3Agrifiti&keywords=grifiti&ie=UTF8&qid=1321129480&scn=705324011&h=4d33378b36d1ffde445aac35dfd3c0b7b814c489Did a search on the forums for "Grifiti" and didin't find anything so if anyone else has posted already, my apologies.
They fit the Poker's and HHKB's exactly, and are really cheap for the quality. If you don't have a crazy OCD about the wrist rest fitting perfectly, you can center align it on a standard TKL (Filco, Leopold, PLU) and it's about 1 inch off each side but perfectly still suitable to rest your wrists. Probably fits Noppoos and Siigs pretty well too.
Edit: Added pics below.
Poker with Cherry Reds
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Leopold TKL with Cherry Clears
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PLU ML-87 with Cherry Browns
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As you can see, it fits nearly perfect for the Poker. With HHKB's having nearly the same dimensions, it should fit them as well. Unfortunately, I don't own one myself, so I can't do a fitting for you guys. On the standard TKLs, it's off a little on each side.
As far as the feel goes, well, it's much better than not having a wristrest. It's a relatively hard foam, covered with material that feel like the old school mouse pads. The height sits a little higher than the Ducky or Filcos, but I personally like it. For $6.50, you really can't go wrong with one of these. If you've got a little OCD like I do though, the fitting not aligning with the standard TKLs is driving me nuts.