It is not even in the Mazdaspeed 2004 Catalog although I've seen the same engine oil cap in pictures of the latest Mazdaspeed versions of RX8 and MX5.
What is the small key lock at the side? Is it the improved design where the position of the cap can be adjusted to align the Mazdaspeed wording to the preferred direction.
I'll have to save some money first only can make offer to you.