I'd honestly like to buy more NVST but I won't sweep my private key to Counterparty. Any decent exchange would work, then I can just send more NVST to my original BTC address.
Bitfinex is non-US based. Kraken is San Francisco based I believe. Despite the fact that their main market is the EU.
You don't have to sweep to buy with counterparty. I bought some XCP in another exchange, made a new account with counterparty and sent them there, then bought and sent them to my original BTC address. Most convoluted process I ever had to go through just to buy some tokens lol