Well, since BA/MRU seems to have a dark side, I guess it's time to remind the community that IBL Travel in Mauritius did seem willing and able to book an AONE4. I didn't follow through because the problems of getting to and through MRU were more important to me than the bargain price, so I don't know how the outcome would have been.
The other annoyance was that they wanted wire transfer. IBL seems a large company with interests in shipping so I wasn't worried about sending money, but international wire transfers are a pita for Americans without a business bank.
When I first contacted IBL "cold" my replies were from a couple of office girls who seemed not to know what an airport was, let alone a OneWorld Explorer fare, despite my attempts to educate them. When in final annoyance I copied an email to "office manager" that person stepped in and proved to be as competent as any I've dealt with. I received what seemed to be a perfectly accurate fare quote within a day or so.
It should be noted that the route I submitted was a very simple straw-man that was not controversial in the least. I always rethink my travel plans and reroute at least once after beginning, so my philosophy these days is to give the remote station something they couldn't possibly have trouble with, nor too many segments for their ticket machine, so I merely asked for MRU-LHR-LAX-HKG-JNB. With that in hand, from a comfortable seat in Los Angeles (or London, for that matter) and a spare USD125 in my pocket I expected no problem in turning the thing into a "proper" trip.
From the (eventually) quick price quote I'd guess that IBL is one of those agencies that considers itself competent to price OWE's. If that's true it might be a nice separation from some of the nonsensical BA rules interpretations. [Aside, CX/CMB seems to be their own pricing guide - the contact there is "Cathay Fares Group" or something like that, and they price almost instantly - faster than CX NAMRES, iirc. Not to compare a TA with an airline's outstation, of course.]
If anyone wants it, I'll follow this forum's convention and pass the email contact by PM.
Happy post-T-day recovery to the U.S. based FT'ers in the group...