You can search on Wheelsmfg for new cones, or at least find some information there. They also recommend taking your cones to the LBS or measure them yourself.

Could your hub be made by Quando? There's a discussion here where you could find something useful.

If you can't find a suitable cone, or if the races are pitted, or if the cones are pricey, then maybe you should search for a new hub. There are plenty flip-flop hubs on sealed bearings, very good and quite cheap, from Formula, Sturmey Archer, Novatec. If you want to keep it on a tight budget, find a hub with the diameter of the spoke holes in the flange similar to yours, so that you can reuse your spokes.

But you may be lucky and find a replacement cone. I love to service cup&cone hubs, as opposed to cartridge bearings hubs, where you just replace the cartridge bearings.