Nevermind, found one!
http://www.aliexpress.com/store/prod...742012951.html
In case anyone's interested, this produces a 185 degree horizontal FOV image on 1/3" sensor format (4.80x3.60 mm) - which on my QHY5's sensor (6.66x5.32 mm) should give me a full circular hemisphere image with no cropping.
Fingers crossed!