Lenses for Board Cameras

[Alan]

Could someone suggest a place to get reasonable priced lenses for
board cameras online? They aren't as easy to find as C mount lenses.

What I am looking for is either a 6mm or 8mm focal length to look down
a walkway. The 3.6mm that came with the camera is way too wide. Also,
are there faster lenses available in the board camera mount, like
f/1.4 ? Or is there a C mount converter that could convert a lens to
board camera mount?

TIA!