For the official Colorado State Tartan I have only found two options. If a 22 or 23 drop will work for you there is a man who sales the kilts at the festival in Estes Park in September. Otherwise it's a custom woven fabric.

As I'm 6'5" and a 22 or 23 drop would be a mini kilt on me, I find myself considering the state seal tartan from USA Kilts verses saving up for a custom weave and a professionally made kilt in the Colorado tartan.