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You can actually purchase it right on here, where it says "wallet" on your profile (top right). An exchange it built into the platform, through blocktrades.su

If you'd prefer a different exchange with better rates, consider bittrex.com
You can trade pretty much any digital currencies there, and turn them into steem.

Cheers, Salman

Thanks! That was very helpful! :)

bittrex.com is an exchange you can buy Steem on but i agree with OP - this should be a hold for the time being, see how things play out. This is just the start and could be really disruptive.