We use KCVDS, which must be downloaded, and also Dueling Network;go to www.duelingnetwork.com. Also, you should download Hamachi for contact, also if KCVDS doesn't work for you.
Technically, you're supposed to PM them through the Hamachi. Most users put up their Hamachi names in their signatures, but for the ones who don't, send them a Private Message here in the Academy. If they accept, head over to KCVDS/DN, and duel them, and post the results in the Battle Arena.
Just saying, it's worth a try, but I haven't gotten a duel here in 8 months, no matter how hard I try. Most people here just don't seem to care
It's still worth a shot, though.