You can purchase PROPY from these places
Go to Bittrex
Bittrex is one of the larger crypto to crypto exchanges offering a large number of trading pairs into bitcoin - including all the major cryptos such as darkcoin, nextcoin and litecoin
Go to Huobi
Huobi (火币网) is a Chinese digital currency trading platform and exchange based in Beijing. Huobi was founded in September 2013.
Go to HitBTC
The most advanced cryptocurrency exchange to buy and sell Bitcoin, Ethereum, Litecoin, Monero, ZCash, DigitalNote, Ardor.
Go to Liqui