GLD is currently on the Cryptsy.com Exchange, so it is relatively easy to transition from BTC, LTC, XRP to GLD on their exchange. There is a 0.29% transaction fee, at least on the BTC/GLD trades, which I think is pretty reasonable, but if you need to do multiple trades from currency to currency, it's something to consider.
https://www.cryptsy.com/users/register?refid=315291Currently, it looks like they offer exchanges to Goldcoin directly from Bitcoin, Litecoin, or Ripple. If you have some other crypto-currency, you'll first need to convert those altcoins in BTC, LTC or XRP and then convert to GLD. Lastly, if you want to deposit or withdraw to USD, then you need to verify your account, which includes a fairly extensive form that includes uploading certain ID and uploading a picture of yourself with a sign and said ID.
Hope this help.