I am also looking for an alternative to arrowroot flour. I am on a paleo diet due to health issues. A lot of my recipies call for it but it does not so nice things to my tummy. I want to stay paleo but I dont like spending all my time in the bathroom.

This site has a wealth of information about arrowroot and various starches that can be used as substitutions:
http://www.foodsubs.com/ThickenStarch.html

Arrowroot is available at Wagmans. Today 16May2014 Wagmans had two difference brands, McCormick and another Island Brand. The price was way too high, about $7 for 2 ounces. I am sure there are other brands which are far cheaper. That said instead you should try using Potato Flour also known as Potato Starch. It is far cheaper and will give the same thickening result. There is nothing all that special about arrowroot except it has a natural flavor and therefore does not change the flavor when used to thicken a sauce.

Besides being easier to find potato flour is far cheaper at perhaps $3 for one or two pounds at the most.

I have use both Arrowroot and Potato Flour to thicken gravy in Beef Burgundy and Veal Marsala without detecting any difference.

Is arrowroot a flour or a powder. I would like to call a recipe flour free but it has arrowroot powder in it . Is arrowroot a flour

I've never seen it marketed as flour, just "Arrowroot." and for some recipes there is no substitute. Although there are other excellent thickeners (potato starch, corn starch, tapioca) arrowroot thickens but the "sauce" stays translucent. That doesn't happen with the other thickeners.

Bob's Red Mill brand has arrowroot flour. I know Whole Foods, Publix and Kroger carry Bob's. At my Whole Foods, it is, as Susan suggests, with the spices, at Publix it is with baking supplies and Kroger has it with the organic products.

Try looking for it again. You probably will find it with spices rather than flour.

You can use any starch in its place. Tapioca starch/flour and potato starch are the best replacements in my opinion, but corn starch will also work. If it's in a gluten-free baking recipe, I highly recommend using tapioca starch/flour.