What exactly is a device tree, and a device tree blob? Where can I get its source code for a particular linux version? I found such name while running linux on xilinx chips (having ARM 9), for example: here
Have you tried consulting the Xilinx wiki?
This howto looks like it has everything you need to get what you want. There's links to a git repository with code as well as directions on how to build it. Here's the command to download the device-tree sources.
The Xilinx website also provides a excellent Getting Started resource if you're new to their toolhchain workflow. Here's a diagram that shows where the device trees fit in:
Given these details a very specific to a variance of Linux for the Xilinx platform I'm not going to include any of the details beyond the above here on U&L, since that wiki is maintained by a hardware vendor, Xilinx, that's supporting that version of the kernel for their hardware products to use.
Seems like this is a completely different "device tree" than the "device tree" under