I was able to get Ritchey replacement rims as parts about 2 years ago. I had to go through a Ritchey dealer (LBS). It may not be worth the hassle, though.
Via email, Ritchey gave me stock numbers for a front and rear rim for my disc mtb wheelset. I forwarded them and the LBS ordered a set. When they arrived, one of them was a totally different rim, with a machined braking surface for rim brakes! 😯
As far as I can tell, both my front and rear rims are identical; there wasn’t a different front and rear as Ritchey thought. I wasn’t too impressed that Ritchey didn’t know their products well enough to be able to send the right parts… 😐