Phil Wood square taper 10mm BB is available. I have one with Middleburns and its a lovely made bit of kit. It is quite pricy but you can service it with just new sealed bearings, and if you have cranks then still cheaper than a full 100mm crankset. My PW has been great value lasting so long, and has only needed 3 sets of bearings in 5 1/2 years of beach riding.
Tim at Sideways should be able to help you out 🙂
Im building an On One Fatty I have Race Face Fatty Chester chainset its an external BB retails at £120 (no Rings) looks ace can be run as a 1,2,3 ringsetup (frame depending) I cant comment on it as it arrived with the wrong bolt – hopefully it will arrive tomorrow so I use it at the Big Bike Bash at Avon Tyrrell this weekend