Ebay seller IC-China has fast ZIF G3s for dirt cheap. They are sold as-is, but for $15 and flat $5 worldwide shipping, who cares? Look under Chips/Motorola and Chips/IBM.
As for finding a Rev B or C ROM SIMM: anyone who is smart enough to remove and sell that seperately is also smart enough to know what they are worth. IMHO it would be best to try and find a full Rev B/C motherboard with the SIMM, as long as the shipping is reasonable. There are other ICs on those boards that are improved over the Rev A - the ATI video for example. You may need to help the seller with Rev identification, so have a search here or on xlr8yourmac.com for how to identify the revision.
As for finding a Rev B or C ROM SIMM: anyone who is smart enough to remove and sell that seperately is also smart enough to know what they are worth. IMHO it would be best to try and find a full Rev B/C motherboard with the SIMM, as long as the shipping is reasonable. There are other ICs on those boards that are improved over the Rev A - the ATI video for example. You may need to help the seller with Rev identification, so have a search here or on xlr8yourmac.com for how to identify the revision.