You can buy coins here at :
alcurex     
Cryptopia   
SouthXchange   
TradeSatoshi   


Considering the way BTC went from $400 bucks to $20,000 , now back down to $15,000.
I have to say there is not alot of liquidity in the crypto markets at all.

However on https://www.cryptopia.co.nz/Exchange?market=ZEIT_LTC alone,
there are enough buy orders to purchase over 2 Billion Coins
and if you include https://www.cryptopia.co.nz/Exchange?market=ZEIT_DOGE, there are enough buy orders on it alone to buy all of the Zeitcoin in existence, you may not want to sell that low , but the buy orders are there.
That does not even include the other markets.

As far as a USD pairing , you have to ask the exchanges, they pick the pairings.

Any other questions, feel free to ask.