If you want to attend a multiplay: host a multiplay.
I hear a lot of this: "please have one in Cincinnati, Ohio!!!! please!" If you want to go to a multiplay event, but haven't heard of one in your area - organize one yourself. Walk into a bar or a chill coffee shop and ask the manager when they get busy on a certain day - then ask to have a 10 person multiplay a few hours before. Take your DS. Show it to them. Be social and seem normal. Fool them. Make a flyer. Use the game finder in the left column of this very site. Get the word out and show up first. Only good, funny, considerate DS owners will arrive and you'll all have a good time.