The NPC textures were most likely made in Photoshop, we know Valve used Photoshop for many of their textures. I haven't heard of any of the source .psd files being officially released, apart from the works by Karen Laur but those were mostly map textures iirc. Then there's the leaks but I'm not here to discuss that.
Is there a particular reason why you'd want the source .psd files?