Well, from his website:
"Clinton uses a snaffle bit on all his horses for both training and riding. He recommends a snaffle bit when performing the exercises from his training videos. If you have a horse that is light on the bit, choose a smooth snaffle. For a horse that leans on the bit, use a twisted or square mouth snaffle to make leaning uncomfortable. Once the horse responds, go back to the smooth snaffle. Clinton’s snaffle bits are blackened steel with silver trim."
This looks about as good for $18: Korsteel Copper Mouth Dee Bit 5 Inch - Statelinetack.com
You could try this at $20: J.P. Cyprium Eggbutt Bradoon Bit - Quality Tack at Outlet Prices - VTO Saddlery
Or maybe a french link at $32: J.P. Hunter Dee with Oval Mouth - Quality Tack at Outlet Prices - VTO Saddlery
Just some thoughts. I'd actually try to borrow some bits to see what he does well in. I like a curb bit in some ways, but it is best to teach the horse what a curb is like before trying it with them. I'm not a fan of twisted or 'square mouth' snaffles. I'm also a total nobody in the world of horses...