In any scenario where we need to find specific equipment, we shuffle one copy of each in the top half of the equipment deck to avoid what happened to you.
This is great advice. I plan to do this every time from now on. I assume you mean that you put all the required equipment in to the top half. So in this case you would put two gas cans in the top half and if you had any more (eg: you own Prison Break) then those get shuffled normally, so you may have as many as four gas cans in the top half of the deck but you are guaranteed to have at least two.
It's worth mentioning that in relation to this specific mission if you have two gas cans only then this requirement also means no molotovs at all. We could really have used a molotov last time I played this.