Originally Posted by
flugvergnugen
At the airport in T1 there is a vending machine next to a column inside the door the metrobus departs from (door... 7?).
FWIW, the other day, I tried to buy a card from both my originating Metro station and destination Metro station. Both were out. Then when I transferred to the Metrobus, I tried to buy a Metrobus card, but both vending machines were out (the attendant told me to wait 10 minutes and reloads were on their way, but that didn't happen). I ended up taking Uber for the remaining 3km down Insurgentes Sur to my hotel.
(I did successfully buy a Metrobus card last time I was here about four or five years ago, so it is possible...but it may not be 100% reliable.)
Great info posted upthread by [MENTION=2612]JDiver[/MENTION]! I'm here a few more days and will definitely be checking some of the recommendations out.