Where to get HCI

I have been looking at you tube and some of the post here. I am curious where I could get HCI. I am in the States and did not know if it could be purchased at Lowes or Home Depot, or somewhere else. I figured I could dilute it down with distilled water to 10% or 4% depending what I was going to make. Just wondered where you could buy it , and what to look for. When I say what to look for is do I need to be concerned about additional ingredients and stuff like that.
Thanks