I assume you mean Marc Bolan. We have established that the dulcimer in question, the one I own, was not Marc's, and we have not been able to find any proof he ever owned one, so he it is unlikely he could have been inspired by Joni Mitchell. Joni's stuff is so unlike Marc's basic rock and roll it would be unlikely anyway. Plus (due to ignorance of how a dulcimer "should be tuned", not meaning that in any kind of derogatory way) Joni used some very unconventional tunings. Marc may well have seen ducimers used in folk clubs in the UK, possibly by Peggy Seeger or John Pearse, anong others.

When I get further info from Nick Odell, I will add it to the thread