I don't remember the name of the after market supplier I used. I think you can find them by doing a Google search. The most efficient valves I found were conical or 'V' type. The best reeds were fibreglass. I put a high polish on the sealing surface and contoured the internals, this gives a measurable increase. I haven't worked on reeds for anything smaller than 100cc.

I think it would be possible to make a manifold to replace the stock manifold that is just a little taller and install a conical reed valve with four triangular reeds. Cut the bottom of the piston port down as far as possible and possibly shorten the piston skirt. This would also make room for a boost port if the cylinder is thick enough. This is one of the advantages of a reed system. One of the best conical reed valves was made for the Power Products Go-Cart engines in the 60s.