25 mm is a standard focal length for micro four thirds cameras (eq. of 50 mm for Full Frame aka type 135). Luckily, there are many lenses with C-mount that would work perfectly. So far I mentioned only Fujian 25/1.4, that was a cheap tool available. Recently I've found a bargain Cosmicar Television Lens 25/1.4 with slightly distorted filter ring and oily aperture, but with perfect glass condition.
Cosmicar Television Lens 25/1.4