There is some confusing terminology at work here.
"DCC Ready" does NOT mean that a loco is equipped with a DCC decoder and is ready to run on a DCC layout.
"DCC Ready" is a marketing term invented by makers of locomotives to indicate that a loco can be converted from DC to DCC operation with a minimum of difficulty. However, it's an imprecise term that means different things depending on the locomotive.
In addition to "DCC Ready" you'll see similar terms such as DCC Friendly, DCC Plug and Play, and DCC Capable. All of these mean that some work is required on your part to install a decoder required for DCC operation.
A loco that has a decoder already installed and is ready to run on a DCC layout is usually described as DCC Equipped or DCC On-Board.
With that as background, Iron Horseman is correct that practically any loco can be equipped with a decoder and run on a DCC layout. At the simplest, some locos are equipped with a plug, and you simply plug in a DCC decoder. No tools, no fuss. At the other extreme of complexity, there are locos whose motors must first be isolated from the loco's frame before decoder installation can even begin. The frames of some locos require modification to fit a decoder, and the individual decoder wires must be soldered to the locomotive components one by one.
For just about any loco, you can find information about converting it to DCC. It's merely a question of how easy or difficult it will be. In general, locos manufactured recently are easier than older ones.
- Jeff