XS Framesets

My son has had some success in Youth E races on his Trek KDR 1000 43cm. Next year he moves up to Youth D and by mid-season will probably need a larger bike.

I'd like to build up a bike based on Shimano 10 speed (to include R700 short reach levers and 165mm cranks) but I'm struggling to find a reasonable cost 46cm frameset new or used.

To-date I've been ruling out compact framesets that state a 46cm seat tube as they equate realistically to 50cm traditional.

Any suggestions on new XS framesets or bikes? Nerd