Here’s a toggle style turn signal switch from some company in Canada. Expensive, but not “MossMotors expensive”.
http://www.specialtycarpartscanada.com/electrical.htm
Paul Mossberg
Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
2005 Intermeccanica Roadster
If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)