After a long search I finally found a company who supply parts for Perkins engines and for the un-initiated they are the manufacturers of the small Volvo marine engines . Volvo paint they green a put the price up 100% or more.
Our local Volvo parts supplier on the south coast of UK wanted £40 just under for one glowplug I got 4 for the same price.
You just need to find out the oridginal engine model, mine is a 2030 and that's the Perkins 100 series engine.
Www.parts4engines. Com
Hope this helps.
Odysseus
Bav38