Attacks » Roll Call
What happens if I have less than three spaces on my bench when using Politoed's "Roll Call" attack? Or what if I don't have any room on my bench at all?
You can use the attack no matter how many Pokemon are on your Bench, but you can only get as many Pokemon as you have spaces on your Bench.
Source: Guardians Rising FAQ (2017-04-22), TPCi Rules Team (2017-05-04)
Attacks » Roll Call
What happens if I use Politoed's "Roll Call" attack and cannot find a Poliwag, Poliwhirl and/or Poliwrath in my deck?
When performing an attack you do as much of it as you can. And since the contents of the deck are unknown you can also voluntarily fail to find one or more of the Pokemon you are searching for.
Source: Guardians Rising FAQ (2017-04-22), TPCi Rules Team (2017-05-04)