No idea about any websites that sell stock engines. I know if you get in touch with Pettit they can set you up with a good aftermarket engine (ported, etc.). Count on spending around what you paid for the car for the new engine though...they're not cheap and Mazda keeps upping the prices on them due to a shortage of rotary cores.

 

You can get a great deal on a stock motor from Malloy Mazda. Also you can check out Dave at KD rotary. He can do the R&R as well. You dont have your location listed.