I'm not sure where you're located.. but.. Dandilion greens I get at my local grocery store. Not all stores have everything - I honestly do the rounds of 3 different places in 2 different towns to get all my greens. Shop around, and make sure you know what they look like since not all stores label everything appropriately. Hibiscus is really easy to grow, so maybe consider growing your own if you're afraid of what florists use to fertilize (so am I!) You can get them at Home Depot around here. I posted on the "feeding cactus pad" thread with a link to who I ordered my cactus from. It keeps great in the fridge. The guy did send me one with roots though so I potted it, and it really took off despite being in crummy New England weather!
I am pretty lucky to be living in Washington State. We have a high concentration of a sorted ethnicity's so I can get cactus pads, prickly pears, hibiscus, dandelions and so many more from one grocery store.
I'm lucky enough to work in a retail garden center. I have to deadhead flowers daily so I bring the flower heads home with me sometimes. I don't recommend picking flowers you didn't grow yourself, because of pesticides and all. I only know it's safe because I know how long it's been since we received the plants and know they are out of fertilizer and pesticide.
As far as Cactus Pad and Prickly Pair .. I haven't been able to find it anyway in SE Minnesota yet