How long is the trade training for a CMT reserve for a ex regular infantry soldier with civilian med quals?

As a quick answer (and i'm not a medic) but it would depend on the time you could take out of your current civi employment as most Reserve courses are designed to be not much more than 2 weeks but there may be a few of them. My advice would be to speak to a local Reserve unit and find out directly - it also depends on what spaces are available, what they need and how quickly they could get you on a course. It's very easy to go to the Reserves as an ex Reg if you didn't leave too long ago and obviously there's no requirement to do any sort of basic training! You may even find that you go on to a slightly higher bounty rate than a non ex reg person!