I currently have no need for these parts, but am posting this in case someone on the list needs a couple.
These babies are used in the first and second generation Apple ][ keyboards. Those are the keyboards without the separate plug in encoder board. MM5740 keyboard encoders are very sensitive to static electricity and can be easily destroyed. Replacements are extremely hard to come by, but while searching around for Apple 1 parts, I noticed a business in the UK that is listing them as in stock.
Note that I have had trouble with a particular batch of MM5740s which I had purchased from Canada a few years ago. That batch appears to be marked rev B . Those particular parts would start repeating characters uncontrollably after warming up. I heard of another person that had a similar experience with parts that were also purchased from Canada. I did manage to make one of these heat sensitive parts stable by gluing a heat sink to the top of the package. For this reason I would limit your investment, at least until you know that this particular batch is reliable.