I have similar problem with Twitter as you. I can follow daily only about 50 people because around 55-60 I get block
It is weird for me that some Twitter account owners said that they can follow few hundreds per day.
On Reddit I'm usong only own subreddit because I was penalized fast for spam in other subreddits.
I'm also using Linkspun and I have no problem to find trades even I have much smaller traffic than you
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Where are you buying traffic plugs for your site? PlugRush?