plumbing vent

[Wild Horse]

greetings ! as i finalize all the major remods getting ready to head south, i discovered a cracked/busted roof vent cover, and i cant find a replacement ! help me out if u can....its my kitchen sink vent, and the cover screws onto a center bolt...easier to screw a new one one than pull up the whole thing. also its a bit larger than most of the caps ive seen, and its shaped like a flat disc, not a cup. thanks for any help !