I think most yacht clubs and public marinas for that matter have already established regattas. At least thats the way it is in my area.
In the case of many private clubs you have to make contact by phone to speak with a representative before entrance. Hence the reason for locked gates. Private is private you know.
As for the local marinas they seem to be mostly friendly talkative sailors where I live. I walk docks to look at boats regularly and find most I meet not only willing to discuss their boat, but usually will invite you aboard to show it off.