Don't know of Brewin having made any Mossie sails. He has made some very nice Bighead Taipan/F16 sails though.

I think the major thing when looking for a Mossie sail is to look to somebody who has either already made competitive sails for the class or somebody with experience in similar style of sails, that is flexible mast cat sails. Which are fairly rare these days, only other class that pops to mind with any real quantity of sails would be Paper Tiger sail makers.