The only place that I've been able to reliably find real 550 (Type III) paracord is at army surplus stores. Other stores (EMS, REI, Paragon) carry plenty of similar rope (~7 strand core, braided nylon shell, ~1/8" diameter, etc.), some of them rated for similar weights. Typically, these cords are for climbers (to secure tools etc.) and for camping, so you might not find any at Dick's.
Hardware stores are iffy, it seems they usually carry crappy thick braided rope for tying tarps up and hoisting buckets of tools.
I've picked some up at a couple different gun/hunting/outdoor stores around here. Army Surplus stores are likely to have it too. But there are some great suppliers online with a huge variety of colors! My favorite is probably SupplyCaptain, but I've got some from several places online.
Locally, probally noy a large variety of colors just the basics, online is the best way. the550cordshop.com has a pretty good selection and freee shipping. You can also get as little as 10 feet up to 300 feet.
Any Army/Navy surplus store will carry the mil-spec 550 cord. Be aware though, the climbers rope is a completely different spec. and will not hold up as well as the 550 cord. If you are planning to weave, create handles, etc... it's pretty fun and there are many different patterns you can create. When weaving though, be sure to take out the smaller white cording that is inside the outer/shell. Do a search for "550 cord" and you will definitely see a lot of shops that carry the mil-spec cord and they come in different colors and patterns.
I always have a big wrap of this stuff in every car and backpack etc...
I have not bought any for a while but I used to buy what was called "utility cord" which is probably similar to what you are looking for. I got it from Adventure-16 (A-16) in California for about $2 (?) for 50 feet. It's suposed to be 400 lb test and was black in color. You might also try campmor.com, pro bass shop, or cabela's. Good luck, Ed507
Not a direct answer to your question, but unless you're really concerned with getting 550 paracord specifically, any climber's accessory cord 4mm and up will be much stronger (at least 2x) and more durable than 550 cord. Outdoor stoors like REI and EMS carry them- I generally order them online from www.bmorescue.com since they're the cheapest supplier of bluewater ropes products I personally know of, but generally accessory cord prices are pretty much the same everywhere.