Most bearing suppliers in the UK or US can get fork seals. They'll be metric and the size should be written on them. Otherwise just measure stanchion OD, slider ID and height. The same sized suspension would have been used for all sorts of lightweights at the time from Ducati to Morini. People like Brancato Engineering and Motori Di Marino will be able to help. If you can get the double lipped fancy blue ones they last longer and are easier to install/remove.