i have a 2004 rx8 6 spd the engine has never over heated and now its eating antifreeze. i know that on a piston driven engine its a head gasket but i just need to know if the engine is shot and requires a rebuild and if it does where can i find another engine for the time in between.

 

Find your problem ? Maybe you just have a leak somewhere, because if you have a water jacket seal leak it will be very noticeable on start up, if it's as bad as you say it will be a pig to start and run very rough, if bad enough it will blow white smoke, see below video of what my car is doing, uses very little coolant but pretty obvious on start up there is coolant leaking in to the combustion chamber.

 

This just happened to my 8. It turns out that I had coolant leaking into the second rotor housing. They pulled the spark plugs and turned the engine over, and it spit engine coolant out of the hole. My car is still under factory warranty, so Mazda replaced the engine under warranty. If not under warranty, you may need to take it to a trusted professional and have it diagnosed, and it could end up costing a few dollars. :-/