I needed this and couldn't find what I wanted, so I built my own to match the neck of my Upton Standard Lam. Feels great! Been thinking of making another, but starting with one of those Chinese kits you find on ebay. For around $210, you get a maple neck (that needs to be finished), ebony fingerboard, tuners, bridge, endpin, lousy strings, etc. Before I ordered one, I'd want to confirm certain specifics of material and dimensions, but this would allow you to finish out an EUB with an UB feel for less than $300.
Check out my "Breaking the Rules" thread for one interpretation of a stick bass.