Here is one thread on harness training from earlier in the year. I'm sure if you searched the forum there are probably more:
Harness training issue | Avian Avenue Parrot Forum
Basically, Aviator and Kaylor are popular brands. Aviator's training DVD is nice. The Kaylor is said to be easier to get over their heads, and my next harness (for Jingo) will be a Kaylor because I want to try the different design. But Opal's is the Aviator and it is a fine product too.
But I don't have any conure-specific advice yet -- need to get on that, really, for Jingo, but right now I'm getting him used to our new Pak-o-Bird, which I already love.