80% of Game Trainers are strictly made in "Windows" programs, so it'll be hard to find one in the first place due to Visual Studio / whatever only recognizing windows systems (Plus, it's made for making windows and ONLY windows programs).
Another option is .swf injecting, there's 3 or 4 programs that i know that are out there; but once again, they're ONLY for windows.
Let's just say, it's REALLY hard to make trainers for OSX in normal terms; if you want, you can just use CodeWeaver or a Windows Program emulator for your Mac OSX System.
It emulates and let's you play (.exe, etc..) and use windows file on your Mac OSX system.
You can google "CodeWeaver", and try the trial. (Yeah, it costs money; or you can be a yarr harr pirate or bucaneer and torrent it).
Or... you can use a Virtual Machine (Google it yourself, this isn't a tutorial).
Use BootCamp and Dual-Boot w/ Windows.
Use Wine, CodeWeaver is the backbone of it and it works surprisingly well; the only difference is that it's Free.
CrossOver for Mac OSX
Remote Desktop (Teamviewer, etc.) But that's only for if you have a Windows AND Mac computer.