There is also another route requiring basic knowledge of Bitshares Light Wallet functionality.
Buy BTC,ETH, Dash... with credit card where ever you can/like.
Download Bitshares light wallet
Register account, make backups.
Send those tokens you bought to your account on Bitshares DEX, using deposit BTC,ETH,Dash.. feature.
Sell those BTC,ETH,Dash... for BTS on Bitshares built in Exchange.
When you sell it, you'll have BTS on your Bitshares account.