It looks to be the same shape as the pickup used on Rockbass streamers, Bartolini make a replacement humbucker. It's the W4CBC shape -
http://www.bartolini.net/information...bass_pu_s4.htm
If you're not into the whole Bart thing, you could probably get a custom pickup done with the same covers (I'd recommend Kent Armstrong personally, but whatever).
Hope this helped