It's a shame that Blitz can't recognize .mb or .ma in the first place.
No game engine can load .mb files directly, any more than they can load .max files from 3ds max. There are sound technical reasons why this is the case, but long story short it's because you want the files streamlined to just what the game engine needs, not loaded down with extraneous crap like you'd get from those proprietary file formats.
Now that Maya supports using Python for scripting, I was thinking of writing a .b3d exporter for Maya. I mean, years ago I tried to write a b3d exporter in MEL, but that proved to be unworkable, but doing it in Python should be much better. Thing is, I'm kind of in the midst of turning my attention away from Blitz (after I'm done with my current project I'll probably use other tools for all future projects) so I don't know if I'll bother writing a b3d exporter.
Still, even if/when I stop using Blitz3D, writing a .b3d exporter would be a fun project and good practice...
yeah no kidding, its been a pain trying to get my maya projects to work in blitz.
For what it's worth, note that the situation now is much better than it used to be (like, say, back when I was trying to write a .b3d exporter in MEL.) The UU exporter for Maya didn't exist yet, so I was forced to use .x for animated characters and obj for static geometry.