We also don't know how many are required.
Is this a piece of equipment being repaired so one will do? In that case, it's not that hard to find a NOS 3240. It may cost a lot, say $10, but considering the cost and trouble of messing about with a plug in replacement board with SMDs, it might be considered cheap. The Buy/Sell/Wanted section on this forum may produce results.
Is this a production run of some obsolete unit for which there's seen to be a demand, so there's an initial requirement of 500? In that case there are specialist sellers of obsolete chips who don't deal in small quantities, or the replacement board approach makes sense.