i have a 72 mustang grande 351c with a fmx transmission. my question is wher can i buy or find the servo spring for that fmx transmision.

okay so I have a little dilemma. I purchase a 72 mustang Grande at an auction and the transmission wasn't shifting. so I took it to a local mechanic to do the transmission work. he send me to get the kit for an fmx transmission which I did. when I went to pick it up and when I paid him he stated that it was going to fail soon due to the servo springs needed to be replace. he stated that it was really hard to find the springs and that if I was able to find them  he can replace it as long as I haven't installed the transmission. so here im lost he left me in the limbo not really sure how the servo spring on the fmx looks like I only find c4 or c6 servo spring and im getting a little frustrated since I have gone to a local transmission supplier where I bough the kit wit no luck. so im reaching to you guys to see if you guy can give me a lead to where I can fin the servo spring/s for that fmx transmission 72 mustang with a 351 Cleveland motor or if there is an upgrade I can do or something I will really appreciate the help.