Curious to see what you have I already did some searching for you
http://www.lumieresenboite.com/colle...Canon_AF_35_ML
http://en.wikipedia.org/wiki/Canon_AT-1
A Petri MT does not seem to exist, but there is an MF-1 or an FT. Given that Petri is a long gone company, you might want to keep whatever you have.