Round geometric registers
These are available in any of the standard designs, except for mission  go to home page

unfinished, specify oak, maple, cherry, or paint grade veneer
suitable for wall or ceiling use

pricing: OK...bear with us here.
    step 1: round up to the nearest inch
    step 2: multiply that number to itself
    step 3: multiply the result by .4
    the minimum charge is $29.95