Hi Mark,
A Data East 500-5035-02 is identical to the Alvin G part. They are available at most of the usual vendors, but BAA usually has the best price on them. http://bayareaamusements.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=TG-500-5035-02R
Edit: I just noticed that they are currently out of stock. Marco does still have some though. http://www.marcospecialties.com/pinball-parts/500-5035-02