Yes the 77 will fit, the only difference between a 77 and previous years are that the 77 levers were painted black. I bought one a while ago from Asia, it was a re-make and it is of dubious quality. It hasn't broken yet but I did replace the bolt with a genuine Suzuki one to improve the reliability.
The last genuine lever I bought was listed here on OzVMXin the "for sale" section.
They are usually listed on Ebay under RM125S, TM125 RM125 1975 etc... and not always TS125 or RM125M