I had trouble finding Baymax earlier this month too. Figured I'd join and post my findings.
From what I was told at my local EB Games when I inquired about it, Baymax was discontinued due to production issues and they don't know when or if they'll get him back in stock. I just decided to order one off Amazon since none of the Australian Online Stores I checked had any in stock or no longer listed him (EB Games, JBHifi, Target, Kmart, Big W, Myer, Toys R Us, Mighty Ape and Gamesmen). I asked at my local JBHifi too just in case the website was wrong (he's no longer listed there) but they told me that only 1 store in Sydney had any left (which was the city store, but when I called about it they couldn't find him).
I'm not sure if it has any relation to the issue some US shipments of Baymax were facing ( http://www.reddit.com/r/Disney_Infinity ... packaging/ ).
Hopefully he'll be back on the shelves eventually, with the movie still in the cinema's people are probably still asking for him. I've noticed that Hiro and Maleficent seem to be selling out too. The only place I've seen them available was Target.com.au about a fortnight ago (which was where I got them from). They're both unavailable now.
Edit:
Also forgot to mention, in my search for Baymax I found that Rockdale Plaza is a goldmine for 1.0 figures. So for anyone that still needs them:
Big W had Mater, Woody, the Sidekicks pack and the Girl Power pack.
Dick Smith had Francesco, Mater, the Sidekicks pack, the villains pack and various single villains.
EB Games had the Phineas and Ferb toy box pack (Phineas/Agent P).