I looked on the Greenhawk sitr and couldn't fine the Pure Source, I have actually tried finding it other places as well and never can... so, here is a product that I used to give my mare, it's a good product, has the same amount of MSM and Glucosamine, I only switched because the stuff I buy now is a bit cheaper, it's kind of the 'no name brand' LOL... so this one is good.
<A href="http://www.sciencepure.com/plus2.html" target="_blank">http://www.sciencepure.com/plus2.html</A>
There's tons of MSM/glu products out there, so I'm sure you can find something to your liking. They also have liquids and I've heard they're good too but I find them messy, expensive and when looking at the amount of ingredients, it seems they don't have as much MSM/glu in them as the product above. Good luck! <IMG src="smileys/smiley4.gif" border="0">
