Weren't the TX500 (and TX300, TX700, and TX900) sold only as framesets?
Vintage-Trek Timeline
EDIT - It looks like the TX500 was built with Ishiwata 022 double-butted chromoly. Fork crown is forged semi-sloping Cinelli type. Lugs and BB shell are Nikko Sangyo long point Italian cut. Dropouts are SunTour GS-11 forged micro-adjusting.
Sounds like a pretty sweet frameset to me.