Servowarm elite 50?

SERVOWARM ELITE 50 - REPLACE GAS VALVE?
Pilot light would not stay on - plumber replaced thermo coupler. Still would not remain on so advised new gas valve replacement needed. CANNOT find supplier for part local or internet searches!! If cannot get part then I am in for a huge bill and a new boiler. Can anyone advise
a] can original gas valve be re-con, cleaned up etc?
b] if not, any idea of a supplier, Lancs UK. Or by post?
Grateful for advice. Regards.
Kennyb.