CVS, Walgeens, and other pharmacies generally keep it in stock.
But I find it rather drying personally and the "comfort feeling" sensation short lived. Adding goldenseal, cayenne pepper, and myrrh powder is supposed to extend that feeling/benefit. But I have never been brave enough to try mixing my own. There are recipes on the internet. Just google it. However I always invisioned such concoctions getting too hot for me or my horse....I was never brave enough to try them.
Oils such as menthol, eucalyptus, sweet majoram,and vetiver can be blended with oil carriers. I love these types of oils to massage on sore muscles. But they are messy and likely too messy for horses.
Wal-Mart has a 'liniment'.. with menthol, camphor, and I forget what else.. right next to the Witch Hazel and wintergreen rubbing Alcohol. It is called 'blu <something/' and is $2.96/bottle. I used half a bottle to half a 5 gallon bucket with water.
I use it on really hot days for immediate cooling. Yes, cold hosing is quite effective too.. but the evaporation of the alcohol and when horse is in front of a fan cools even more.. and lasts longer than a cold shower.
I've also used:
1/2 bottle witch hazel (Wal-mart)
1/2 bottle Wintergreen rubbing alcohol (Wal-mart)
1 tsp menthol crystals (dissolve in above mixture in advance) (Mountain Herbs)
2.5 gallon cold water
This one provides the same 'tingly' feeling as store bought liniments.. at a fraction of the price. It's stronger with the menthol crystals than the first one...
I won't pay much for a liniment.. cause, well, they are so short lived.. but, if nothing else, they feel good to me..
I rarely use liniment anymore (because I'm lazy and my show horse is at the trainer's), but one I used to use is equal parts rubbing alcohol, witch hazel, and cider vinegar. The cider vinegar also seems to repel flies just a tiny bit.
You can mix Dollar store blue mineral ice with alcohol for rubbing legs- The mineral ice thickens up the alcohol just a bit so it's not so runny.
Rubbing alcohol has gotten expensive in the past few years- I remember buying it on sale 3 bottles for a buck. I haven't looked since I haven't been in a liquor store in a while, but I'm wondering if really cheap Vodka or gin in plastic jugs would be cheaper, I mean, it's not like it's fit for drinking! Witch hazel is also one of those things you have to shop around for- I never buy brand name- last time I looked Target was cheapest.
For menthol crystals I know Big Dee's Tack has them, also try eBay for them, as well as camphor and oil of wintergreen.
I have to second another post that suggested NOT using liniment at all. It just makes you feel good, has no effect other than a little skin tingling. There are a few exceptions. Sore No More which has Arnica will actually reduce leg filling quite a lot. And works on bruises. I use it on my wonky knee that has fluid under and around the knee cap and it it does help me besides my horses. The person who adds vinegar to her liniment has at least one active ingredient in her liniment. Vinegar does help to prevent or kill skin fungus of various types. It works on athelete's foot quite well.
A detriment to many liniments is the ability to burn a horses leg if you rub it on too vigorously or against the lay of the hair. Sore No More doesn't cause a burn. I find a ver small amount goes a long way but I'm not using it across the entire body, just where it's needed.