I am not entirely certain what "BSP seal washer" means, sounds like a" dowdy" washer to me ( metal washer with plastic insert ) if so I have found them at ACE Hardware.
thanks, I will start my search, also will check with our Parker hyd. warehouse We are building a large enough inline gauge for old eyes to see better. Should be more accurate also.
These are actually called Dowty Seals, named after the company that made them - an alloy (usually) washer with a vulcanized rubber inner ring. Originally made for the aircraft industry but commonly used in other pressurized systems.
I could bore you to death by describing exactly how they are made...