Yeah..sorry Fluffywolf, I don't think there's going to be a "This is how all INFJ's shop" way.
I don't like running errands, so I just want to get in and get out as quick as possible, and I'm not really there to strike up conversation. Guess I'm not friendly in that regard, although if someone makes a comment to me I'll smile or make a brief comment in response - but I'm definitely not one to engage. ;-). Grocery shopping is a chore for me. I might look spacey around the vegetables and fruit, deciding what looks fresh and what I really want to get, but other than that, I pretty much know what I'm going to get before I go, and am on a mission to get it done and leave. :-)
Where to look? Eh...I don't know that generalities are all that helpful. I know several INFJ's and we have varied interests. I don't know that we're the most approachable people though - esp. w/ regards to strangers coming up to us.
I'd say if you're interested in one thing, then start doing that. Common interest groups are good ways of meeting people.
We're everywhere (and nowhere), I tell you!!