OpenGL is an open library and there are many opengl implementations for different platforms. We can get their source codes. Are OpenGL software requirements documented and public distributable?
Your best bet is to read the licensing details on http://www.sgi.com . Mostly it is licensed for hardware manufacturers, but I do not believe any source code for OpenGL. If there is a software implementation like MESA then its licensing and copyright is owned by them.
Hope this helps.