Those can be ordered from any Rowe distributor. A list of authorized Rowe distributors is on the Rowe website and there's probably one near you. if you don't know the part number (or have the manual) just take the OBA with you to your nearest Rowe distributor's parts department and point out what you need. Chances are it's in stock or can be ordered from Rowe. Rowe does not sell direct---you must go through authorized Rowe dealers/distributors.
Remember, the OBA was in production a very long time: 1968 thru 2005. Parts are plentiful. I feel it's the best and easist to service bill acceptor ever made.