Well, Hamachi is widely used in DA to duel the people you want and also serves you well if you can't host with IP. You'd better download it, all the important information and the official DA Hamachi networks are posted here by MUFC; http://www.duelacademy.net/t5779-duel-academy-s-starter-guide
Still, if you'd like to duel specific people you meet here or in KCVDS you can start by creating and sharing your own network. Remember that there is already a thread so as for the members to post their own one; http://www.duelacademy.net/t1377-what-is-your-hamachi-network