Short answer: I never put all my eggs in one basket...
Longer answer: Look on the bright side, the shop let you know before you showed up only to be surprised by the non-availability (and why I always have the Wechats for my regulars, or potential regulars so they can let me know of any problems). Given I was a visitor, I wanted to make the most of my time in SYD, so had a regular for 6 out of 7 days. Several of my regulars only work one day/week at the shop I know them at, and I don't know where else they work. So, if she calls in sick on MY day, then I have 2 options:
Option A: Pick a regular that does work multiple days and IS working on that day. Yes, that can have a bump effect: so do I see the secondary target twice in the week (and some I have), or do I go to Option B on the secondary target's usual day giving me some time to plan... Plus points to her if, at short notice, she does have time for me.
Option B: Try out a place that is on my "to do" list. I do keep a virtual notepad with places, names, phone numbers, so will give a potential a shot (pun intended) at a position on the starting rotation.