MRP used to have that as an option on some,of their forks. The Loop if I recall. It couldn't hurt to reach out to them. I recently had a straight steerer replaced by them on an older WhiteBros Fluid 135.
Ritchey uses (used) a IS42 standard which is not compatible with those tapered fork conversions. You need a IS44 at least.That is going to be tough to fine for a good fork, but you can get headsets that go from frame setup to be a straight steer to a tapper one.
Oh I'm used to bikes with a IS44 which does work for the conversion, bummer that IS42 will not work.
As others have suggested, Manitou Markhor, and should you want more damper tunability you can buy the ABS+ damper to upgrade.
Also, beautiful bike. I had an opportunity to snag one a while back, but didn't and missed out. Still haven't really got over it...
MRP Loop SL is available in both tapered and straight steerer.I actually emailed them earlier today. I did not see that fork listed on their site anymore. I know in the past Fox swapped out the lowers for people but when I called them they said they no longer make anything that would match.