I've started a thread on Facebook that shows collectors where to buy all the coins seen in the series and I'm going to post a coin here each time I post it there. There are about 20 coins used in the series which can be had online as individual coins or in lots.

One of the most iconic is the Yuan Xiao Tou Min guo 2 year. It appears in the Firefly companion books and is one of the most common ones used in the show. It is sometimes called the 'fat emperor' and you can buy it in lots of 5 for around $10 or less. It's the best deal I've found for that coin. You can buy them individually, but they often cost $5 or more for one, so the lot gives you extras. If you get no other coins for your collection, this is the one to get.

http://pt.aliexpress.com/item/Big-promo ... .35.gWBWzC