this post is a little different to your norm, so I'm not expecting much.
I'm partaking in a competition where we are building a chain driven wheelchair and currently have it set-up using bicycle wheels with threaded 19T fixie sprockets, however we need to slow it down. Commercially, 21T is the max number of teeth I can find but require around 34T. I can get some custom made at a lot of cost, but does anyone here have any other suggestions using items that are already available on the market, if there are any? I've seen bolt on fixie sprockets, but they require the hub to be changed.
Any help would be greatly appreciated!