Good question. I know there is a member of NASIOC who every once in a while will do group buys on embroidering headrest covers (doug-e-fresh maybe?). He'd have the information.
One thing to consider is that he's been having trouble getting Subaru to let him use the actual WRX and STi logos. They are copywritten. Also, while the WRX looks like it might be a font, the STi logo looks more like an actual design. If you want to go at it yourself, look into Adobe Font Folio 9.0. It has something like 2700 fonts. If it's not in there, I'll bet something similar is.