Websites such as TradeDollarNut.com, TradeDollar.org, Wikipedia and eBay have information about trade dollars. Some books, such as "A Buyer's Guide to Silver Dollars and Trade Dollars of the United States" have a lot of information about trade dollars as well. TradeDollarNut.com has general information about American trade dollars, rarity factors, values of trade dollars, condition census and historical auction prices. There is also a detailed description of trade dollar coinage from 1873 to 1885.
TradeDollar.org offers information about United States trade dollar compositions, specifications, mintage and proof trade dollars. There is also detailed information about rare trade dollars minted in 1884, 1885, 1873 and 1878.
Wikipedia offers information about trade dollars from France, Japan, United Kingdom and America, as well as info about the general history of trade dollars.
"A Buyer's Guide to Silver Dollars and Trade Dollars of the United States" includes detailed descriptions and histories of all types of silver dollars. Descriptions include current pricing, mintages and estimated number of coins remaining.
EBay features guides, which include pictures, that provide information on detecting fake trade dollars. The information explains the types of obverse and reverse sides that a genuine trade dollar might have, as well as possible combinations of the sides.