After a looong search I came upon this precious gem:
A Mac Emulator for the TI 99/4a - a machine designed around a unique
CPU, the splendid TMS9900.
++++++++++++++++++++++++++++++++++++++++++++++++

Choosing a TI99 emulator for the Macintosh

MacV9T9 requires at least a Macintosh with 700 kb of free memory,
system 7, and Color Quickdraw (which requires a 68020 itself...). It
seems that it is too slow to be used intensively on a 68020 or 68030,
but I don't know where the limit exactly is. It runs natively on PPC.

One important point : you will need some copy of a TI99's ROMs. Don't
worry, though, they should fall in public domain soon (around year
2006 ![Wink][1] ).

Oh, yes, I almost forgot : this program is a freeware.

I have not released the source code publicly yet, since some things
are not in final form, but you can ask for it.

Compatibility
Architecture: 68k PPC

  [1]: http://macintoshgarden.org/sites/all/modules/smileys/packs/Roving/wink.png (Wink)