The short answer is that, if you haven't found those constants in the same place as the rest, they probably don't exist. Although I'm not sure, and there's always a way to find those values out. Such constants aren't required by the C specifications; whether they're defined or not depends on the implementation (compiler) that you're using.
In C, not even the bit sizes and ranges of data types are defined uniquely. For example an int will be 32 bits long in a 32-bit environment, and 64 bits long in a 64-bit one. Most more recent languages do specify fixed sizes and ranges for all data types, but C is different in this regard.
PS: there's a sub board for this:
http://www.abandonia.com/vbullet/forumdisplay.php?f=25