The replacement ribbons seem to still be manufactured, and cost about $6 each.
The Brother AX-28 Typewriter User’s Manual. (handy for figuring out all the funky functions and modes)
Mr. Martin’s Typewriter Museum. Scroll down to see his Brother AX-28.
Some Other Links to nifty typewriter news stories I found today:
Hoflander: in love with the typewriter
Manual Typewriters Survive with Collectors: Sacramento Bee