I'm pretty sure you need a script in the US to buy it OTC. Progen usually has it but they've been out for a while. They're usually my first choice. Otherwise there a few other retailers online but shipping is usually outrageous.
I've always wondered this. I mean obviously years is probably a good time to toss it. I've read that as long as it's sealed and unused it will last a very long time. Keep it in a dry dark place, like a hospital would. I've heard once it's punctured you got a few months and keep it refrigerated. I honestly don't know if that makes a difference or not. Hasn't failed me yet.