You are, maybe, trying to optimize too many things.

You could tell these other people about the LBS rides...

Or, you could basically create a club and publish a list of various types of rides at different levels. There aren't going to be any magic ways of excluding unprepared people.

Another way, is to start with some ride and see who shows up.

If you make the requirements clear, be prepared to disqualify people who are not prepared.