First of all: Do they want to make real live friends? having only internet friends doesn't sound too bad, does it?
they have tried to socialize in a fishbowl event but they weren’t able to get a friend there as I feel it.
you don't get a friends from a single event. give it more time. much more time. some other comment mention hobbies or groups, and i think this is the key: you don't go to those events because you want to make friend, but because of you interest and you make friends by accident. Don't pressure it!
public library
here the subscription fee for one year is about as expensive as a single book.