I did mine through an Institute of Technology, which is what TAFEs call themselves when they want to look and feel more intellectual than TAFE. There are plenty of shorter courses through private colleges, but they generally cost more, and the quality of the education given is...questionable. I remember, back while I was doing my Cert IV and Diploma, being told that at AIF the subject on exercise programming basically showed them a program, and then got the students to write the program back to the assessor. That's equivalent to teaching someone the PTC beginners program in the stickies, and asking them to recall the program, and if they can, saying they know how to program. Naturally, the real test of a trainer's ability to program begins in their understanding of why a given program works and their ability to change things to accommodate different needs.
My Cert IV was 1 year full time, face-to-face. To do the same course part-time and via correspondence could be 18-24 months. Again, you can do much shorter courses, but I couldn't tell you which ones are worth it.