It (GCG)is hard to find tincture, but it is available as a dried herb where ever a larger oriental population exists.
I goto Windsor Canada (sometimes Toronto)to get my supplies of dried herbs: Golden Coin Grass ($40/pound), Coptis ($8/ounce), Curcuma ($8/pound), and Chinese bitters (Chinese gentian+bupleurum).
I use a blender to pulverize these roots/leaves/stems and make my own tincture using 100 proof vodka--the process takes 2-4 weeks. I just made 2000ml (that is 8 250ml bottles) of Golden Coin Grass Tincture for $38 (2 liters of vodka at $9/bottle and 1/2 pound of GCG at $20.
I am willing to provide you with the recipie if you are interested and I have an extra 2 ounces
of ground coptis root, and 1 pound of dried, whole gold coin grass (dried herbs keep a very long time without losing their strength)for my cost plus shipping to help you out.
I got very little info from the internet on these herbs, but did find plenty when I got into a town with a chinese community--lots of asking questions, footwork, and searching. Language barrior is a problem also as a lot of these little mom/pop herb stores do not speak english.
Hope this helps--email me if you have any questions--link should be active.