Well, the good news is if you were considering Pyrocat or Rodinal, you're probably best off trying D-23. Pyrocat is not really a compensating or low contrast developer for this type of application unless it is used in stand/semi-stand procedures (at least reportedly). So I don't think you'd gain much there. As for Rodinal, it isn't a compensating developer either, although some people report contrast reduction when it is used in extreme dilutions. It also tends to actually decrease film speed slightly vs say D-76. So again, I don't think you're missing out too much. In the end these are still general purpose developers.
But, I don't want to discourage anyone from experimenting. It never hurts to try something (on a spare roll of course), so you have nothing to lose by trying D-23 at say a 1+3 dilution and see what happens. Maybe it will give you the results you're looking for with the x-ray film. Maybe a two-bath procedure with D-23, or a Windisch or Beutler compensating Metol formula. If you end up ordering from Formulary, something like FX-1, FX-2 (or TFX-2) might help you get lower contrast with reasonable film speed. But I agree these are not very economical solutions unless you bulk-mix yourself.