Any Olympic recurve riser and a good set of limbs. Not sure if buying them from Lancaster Archer changes your chances.
The riser is complex as there are many manufactures represented in the top competitors. That suggests it is more to do with the individual archer than the riser itself. You will find that Hoyt, Gillo, W&W, CD, Uukha, Spigarelli, and others are used very successfully. Some riser are built with barebow in mind by have a weight system designed for the riser. By even a non-baretow riser can take weights--I use a Hoyt Xakt. The bottom line? Buy a quality riser. (A piece of advice from one of Sweden's top barebow archers is to chose the color that you like the best.)
One new change in the barebow rules since yesterday now allow weights above the grip. How this will influence new barebow designs is unknown? I have experimented with weights above the grip and now set up my riser with them. I know of a couple of top European barebow archers that feel it is a significant change. Naturally, there are barebow archers that think it makes no difference.
If you are just starting in this class, start with inexpensive $100 WNS limbs to get experience and figure out what you want in a limb. You are also going to have to figure out how to tune your arrows and bow using a crawl in string walking. Note, all winners of Lancaster have been string walkers.