In case you have some sort of Pep-Boy or Autoparts nearby: The solenoid out of the old Suzuki SJ410/413/Samurai and 1.0 or 1.2L Swift (check the part no. there are various versions for the swift, only the one which is also applicable for the old Suzuki 4x4 will do) or check the breakers for one. Furthermore, in case you're at the breaker's: The original TR1-starter is identical to the one found on the 1978 and 79 Toyota Celica.

(You're form OZ, right... if not ignore the last comment, because everywhere else in the world it's highly unlikely to find a vintage 70ies Celica...)

Cheers,
Greg