Since this thread got resurrected, here is what I found when I was looking at this... some of this has been said, and some hasn't.
If you go to http://nissan.navigation.com/product/Ca ... ssanNA/USD
you can buy the SD cards for $179 yourself. You need three things:
Unit Code: This is what shows up as "SET" on the "NO SD CARD" screen
Serial Number: This is "SNO" (hence the name: S for Serial, and NO for Number)
Confirmation Code: This is the one that no one seems to know how to derive from the "NO SD CARD" screen. NAVI-1 doesn't seem to share the same format as the Confirmation Code field (it might be the most recently loaded Program Version?), so that's where there's a problem. With more data, we might find that the confirmation code is just a checksum of the other two so that you don't accidentally typo the others and get pissed off when you get a card that's not for your LEAF. However, I only have the data from my own LEAF, and it's hard to derive the algorithm from one sample. I haven't tried removing my SD card to verify these things -- I should get around to it one of these days.
EDIT: Confirmed that my "NO SD CARD" screen shows the same thing as my Navigation Version screen for everything but the Confirmation Code, and that NAVI-1 is the same as Program Version. So we just need to figure out what the Confirmation Code algorithm is, and then you can just order the cards directly from the update site. (Maybe someone should call them up and ask if you even really need to provide the confirmation code, or if they can sell you the update with just the other two pieces of info?)