i myself was interested some time ago in getting mud skipper's, trying to find one as you have found out yourself is dire situation, I found 1 pet shop of all of auckland, in which the guy went out of his way to find out from the supplier if he could get it, which he could at the cost of about $80 (seems abit expensive side, but given even HFS weren't interested at all in helping me, knew the chances of getting one myself outside of this guy would be impossible unless you play the waiting game, i didn't end up getting one due to loss of a fish tank to unexpecting fry pitching up).
Now this might be of no help and i really can't remember which shop it was, but here is the link i am 99% sure i used and phoned around.
http://maps.google.co.nz/maps?oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&q=auckland+pet+stores&fb=1&gl=nz&hq=pet+stores&hnear=auckland&view=text&ei=ydISS-HKFYW4swP6qsnmAQ&sa=X&oi=local_group&ct=more-results&resnum=1&ved=0CBwQtQMwAA
best of luck, let me know if you have any luck