Bespoke Parts, usually made for Midges
New(ish) Ok Poor
Radiator surround £70 £50 £25
MOBC badge (Hex) £7
Midge badge (oval) £5
Generic
Headlights (pair) £200 £50 £10
Narrow Seats (pair) £80 £40 £10
Mudguards
Some addresses that might help with bits and bobs
SC Parts (brace yourself) don't forget the hubs, spinners and nuts
MSW Used to be more expensive but I'm not sure now. Wider range. Check both.
Instruments, I found Mayhill tractors very reasonable for stuff, although their prices don't include VAT or postage (The ignition switch is rubbish though, and the instruments don't all have illumination)
These are just a few, and of course there are many alternatives. More later.