If you're not happy with current SLR offerings, I guess you could always build your own. Denis MO's project is pretty mind-blowing. "My project consists in creating a 24x36mm reflex all by myself, no more, no less. I have had this project in mind for the past 25 years, but I didn’t master the technique nor did I have the knowledge necessary to complete it until now (I’m almost 42)." Impressive on many levels.
For a more detailed explanation and many more photos, look here.