Rx7/Rx8 & 20B Water Jacket Seal Kit
Consider an O-Ring Kit, its a cheaper alternatives that is more inclusive:
The above linked gasket kits include these water jacket seals AND, tension bolt washers, dowel pin o-rings, intake gaskets, exhaust gaskets etc, etc, a great value.
Mazda Water Jacket Seal Kit, enough to do a complete engine.
Don't be fooled by competitors "teflon encapsulated" o-ring kits which are comprised of nothing more than a few o-rings straight out of a Mc Master and Car Catalog which were not designed for the rotary engines at all, and happen to be relatively similar in size but were originally developed for a diesel engine.
We have personally seen competitors teflon encapsulated water jacket seals ruin multiple engines. We have also seen the teflon encapsulated o-rings fray and be useless after 10 minutes of idling the engine. Don't get cheap on your rebuild, save yourself time and money.