For any Heathkit alumni, there are just 5 XTB-523 kits left. There are still plenty of assembled units available, but these are the last of any XTB kits.
Still in stock are the XTBR, XTB-523, XTB-ANR, XTB-232, & XTB-F15+. There is only a handful of the latter two left.
Jeff
The problem is that your stuff works very well and never breaks. I have no need to buy more! :-\