The chances of getting the SD that you want by farming are negligible. I think it's even more probable to summon Darion directly from a L/D scroll ( I've done several times already :D )
Your best chance is to watch the forums on Sunday and sending a Friend Request to the players that get the Vagabond SD then asking him/her in the chat to accept it. Use their name to catch their attention and do it once or twice, no more. That way you are showing real interest. Most people will have their friend list full or near full and does not really need new friends, they have to get out of their way to go to the particular screen and accept so if you are not respectful they won't take the time to do it.
I personally prefer this to the constant bugging people usually do by spamming requests in the chat to be added as friends. That shows only laziness (in my opinion). Moreover, most people adding you will not have a SD at all.