@TheSprinter85Pack rat and fantastico (foot soldier and 80s elusives for town center plants) spawn in specified locations (fantastico seems to be 100% spawn rate and he spawns near the bridge that goes towards the mountain, just go to the bridge then go right, meanwhile packrat isn't a 100% spawn rate, but it's still fairly high, just visit the sewers once in a while and chances are he'll be there), squiddy just spawns in randomly when battling in pressure pier, which is what made squiddy difficult to find for me and many others, just wish popcap would make elusives a little less "elusive", I'm willing to bet some of the younger players have 49/50 medals on some campaigns as well for this reason.
Also @TLEsquire @spIash_damage ...where exactly is the taco place? Do you mean one of the buildings with signs on them? Or do you mean a place where you can farm tacos? I'm sorry for sounding a little bit dumb but maybe a screenshot of the area and the part of the map you're in would help?