From what you've described, I'd rate that as a +3 total - researchable, if you've got the right sorts of sources, but not something you could find with a simple paranet search, and something just about anybody could get a hold of if they really had to. (Heck, you can find instructions for how to home-make stuff like dry ice on the internet; it's not something most people will have just sitting around, but it's not hard to get if you need it. Though this may vary by location, now that I think about it - for example, if your game takes place in the jungles of Africa, cold as a catch might deserve only a +1 for accessibility.)
However, it's also pretty narrow for a +2 accessibility catch; were it my character, I'd tend to add at least a little something more, like some of the possible chemical type attacks people have mentioned. Doing that isn't required by the rules, though; it's just my own personal preference.