Just start up a conversation with the divers parked next to you. For the most part, everyone is pretty friendly, and if you are straightforward with them, would allow you to tag along. Now, if the group beside you are all diving rebreathers, I would probably move to the next vehicle. Not that they aren't friendly; just probably a bit above the diving you will be doing.
I would also check in with Wazee Sports. I'm sure that they have "fun dives" and whatnot that you could participate in. Go to their web page, or call them. I'm sure that they would also direct you to local dive clubs.
Which wall were you diving?