Same issue a buddy faced leading him to go the S&S route.
Grooved split flange couplers are a common, standard item, granted not necessarily the most precise components unless you find one used for cleanroom or high pressure gas. Finding one in the required size (and without the compliant ring inside) may be the issue.
I suggest contacting Ritchey, they have sent me detail drawings of every part I've asked for. If you have the critical flange dimensions you "may" find a standard coupler that will work.
