It looks very much like the later Knott Avonride 'Waterproof hubs' which have a rear seal fitted as well. These were on a replacement axle fitted to my old trailer in 2013 and quite different from the original
I couldn't find a source for the rear seals as most seemed to be 72x53x
10 but got sent 8 for free from Knott in Burton
Knott Avonride waterproof SFLbrg hub assy 5 M12 on 112 PCD
Knott rear seals p/n 114196 SOG 53 72 8 (72x53x8)
I sold a spare set of hubs c/w new bearings and about 6 seals to Rogue Wave so he may be able to help /sell
If he or Trailer bloke cant help, then Mersea Trailers should (just make sure they know they are the SFL hubs)