You can buy UNITY (12071612744977229797) on the NXT Asset Exchange.
To access the NXT Asset Exchange you need the NXT client: https://nxt.org/download/
To buy UNITY you will need NXT, which you can buy on several exchanges, ie. at https://bittrex.com.
SuperNET/Unity is a dividend paying asset. That makes it different than a normal cryptocurrency and that is one of the reasons it isn't listed on another exchange other than NXT asset exchange
One of the future steps is to integrate all SuperNET assets into Agama. Once that happens we won't need another exchange.