A couple of people have been in contact regarding the search for a small remote filter unit. Steve sent these two pics of, what he believes to be a late 250 Triumph/BSA unit.
This gives a far better idea of what is being sought, probably half the size of the far more common Commando unit and the universal ones that are on offer, thanks Steve, hope it helps.
Craig from Birmingham also mailed to say that the unit fitted to the LE Velocette is another compact option, that he has successfully used in the past. Cheers Craig, that will broaden the search and may turn up results.
Another lead came through The Jockey Journal regarding a Daytona Project back in 2003 where a guy at Vokes actually re manufactured 3 units. Whether or not that is possible any more, will have to be found out.