Oops.... I'm just about to answer you which restaurant's jellyfish tastes the best...... (J/K)
I only see beautiful jellyfishes in aquariums, other than that, I never seem them in shops wor. I would like to "pet" them too ar.
i remember watching a something on TV saying that there are many people wanting to pet them but not having enough skill to take care of them safely, and end up hurting themselve.
I hope you really know what you are getting before you try to pet them. I assume you are probably not an expert on that since you are asking the question in such a general forum.
http://www.jelliquarium.com/ may help you.
They need a special tank (the filtration) to start with since they are suchd delicate creatures. You don't want a current that's too strong otherwise it will get sucked into the filter. You don't want the water to not move at all otherwise the jellyfish will be suspended. You need the right current to bring it its food (zooplankton).
I don't know who sells jellyfish in vancouver. They were sort of a hit in HK few years ago when they were sold in little jars in Mongkok.