I hear this a lot though and a lot of people are just going about this wrong.. My tips:
Don’t go for Bella (or any SD) until you can get through B7 in under 40 seconds. This can be easily done with 3 L30+ AOE damage dealers (Grim Reapers, Magical Archers, whatever), a healer like Kona or Colleen and a buffer like Shannon. Once you get through B7 then quit the battle and start it over immediately. If you cant get enough SD tokens in one shot (one 60 minute span) you are kind of kidding yourself.. You need the tools to do the job, so focus on them first.. This should not even be a concern until you are level 35 or so.. You have too many other things you should be doing to build your account to worry about SDs that you are not prepared for..
Then, you just sit in an active chat channel and be patient. Don’t spam the channel telling people you are there. Sorry, but no one really cares – and they will probably just mute/block you. If an SD opens you will see it. Try to friend request the person.. If they are already full then move on and go back to waiting.. Don’t expect anyone to delete someone from their friends list for you, that’s just rude.. And if you send them a request and they don’t accept then just move on.. They are busy doing their own thing and aren’t paying attention to chat – that’s normal.. It never took me more than an hour or so to get into an SD that I needed. No, i didn’t get into every one that came up.. But another one will come up if you just give it some time. It also never took me more than an hour to get the mon I wanted from that SD.. Sometimes I could get 2 or 3 from the same SD and I could use the extra for skill-ups. You just have to be prepared, be patient and be polite..