Generally speaking Etsy is the place for this. Depending on how complex you want it to be it can be relatively cheap or as expensive as some jewelry.

Jen Green Headbadges makes some wonderful mixed-material examples.
Mediterrantio has some cheaper novelty headbadges for modest amounts.
VintageBikeStore has original headbadges from old bikes.
WendelinWombat for novelty stuff as well.
GabinandCo for lots of vintage French stuff

If you want cheaper than $35 a piece... it probably doesn't make any economical sense with the complexity of some of these vintage models.