Okay...my biggest suggestion for the Epsom Salts is to chase it with water. Drink it quick, don't breathe and chase it with 1 or 2 glasses of water. This helps me alot. I haven't done it any other way so I can't help you with the other questions.
As far as the ornithine, I have never used it. I have done 3 Liver Flushes and I've been fine. Granted I haven't sleep like a log or anything but I haven't been up all night either. I really don't think it is necessary. If you do want to use them you can buy them online. Just do a google for ornithine and you shouldn't have any problems finding them. I haven't every used HCI and don't know what it is. I don't think it is necessary either.
The Black-Walnut tincture is pretty easy to fine. You should be able to get it at any health food store, whole foods market, vitamin shope or maybe even GNC. You should get a tincture of Black-Walnut hulls, Wormwood and cloves. I got mine from vitamin shope. Hope this helps.