This claims to have it:

http://www.ntua.gr/electronics/hwb/connector/storage/macfloppy2.html

here's another one:

http://pinouts.ru/Storage/macfloppy2_pinout.shtml

But I'm not sure if those are correct as pin 9 is +5V as listed there, and 20 is "N.C." Or Not connected, so that's probably wrong... OTOH, http://docs.info.apple.com/article.html?artnum=18207&coll=ap has the same pinouts, so it might be +5V and N.C. but possibly they mean something to the drive to allow single sided use, not sure.

Anyway, whatever you do, make sure that it is reversible.

You could try ebay item number: 220177665009, but I'm not sure if those are superdrives or 800k drives or what, or if they're even working drives. The cases are a bit too modern, so they're more likely to be superdrives or 800k drives than 400k drives.