What the hell is it with this game? Why is Portable Ops Plus (which, from what I gather, contains no story mode at all) available practically everywhere, while the original game is nowhere to be found? There’s one or two used copies on Amazon US, but none at all for Canada, and no online or “real life” store I’ve ever seen carries a copy. Barring eBay, is there any way at all to get hold of this?
Cracked PSP, ROM, memory stick. 
Out of print good games = sucks to find.
Not interesting in cracking my PSP or purchasing another memory stick. I have a 32MB one which works perfectly fine for game saves, which is all I intend to use it for.
What Zero said is your best bet. I’ve played two or three games that way. Just a get a cheap little 2GB card and you should be good. If not, then just keep looking.
Portable Ops+ was more or less fan service to the people who played it online. I never bothered to buy it.