Been meaning to fix this thing for a few weeks, and today an idea dawned on me. Rather than try to find the exact part of this obscure Chinese scooter, just use this "medical bottle" (Dont know really what you call this...)
Mostly all I had to do was drill some holes in the cap of the bottle and cut down the plastic reflector around the bulb with a Dremel. A little hot glue and this baby is watertight. I also spray painted the cap black just so it was a little less conspicuous.
Works great, score one for random junk!