not sure if anyone has this but looking at the links on this page, it certainly does exist!
Seems there was a bootleg VHS tape some time ago that features Sam Jones original voice before it was dubbed over by a mysterious actor when the star and director fell out and Sam didn’t get called in for post production.
Links are here -> https://sites.google.com/site/flashgordonmovie/flashgordon–dubbingmystery
I’d love to get hold of that audio track on the tape and give it a listen