1966 bar plates

You can try to get information from the Orioles fan club. Go to MLB.com, click on the team site for the Orioles and click on "Fans".
Alternately, you can contact a reputable auction house (for instance huntauctions.com) though you should keep in mind that auction houses are not in the business of dispensing free estimates.
In either case, you should have a photo of at least one of the plates if not the entire set. It's hard to get value info without a visual.