Any question answered...

If by brake mounts you mean cantilever brakes, Old Man Mountain racks are probably your best bet. Mail order across country lines and even oceans is easy these days, and for me usually half to two thirds of the local price. (I will pay local if it's HERE, but the item almost never exists out here in the hinterland, and most LBSs are loathe to do special orders)

At the moment I have a rack which is fastened to the rear brake bridge, I don't have canti mounts or rack mounts.

I've since seen that you can get racks which fasten to the seat tube or seat post - anyone got any experience of these?