Tonya, I do believe that both McCall's and Simplicity carry "patterns" for slipcovers. These are the two biggest pattern company's and the easiest to follow. You may not get a pattern per se, but rather directions and ideas for different styles (ie, boxy, formal, country). They are fairly easy to make, but my pet peeve with sewing is that it is usually cheaper to buy one made from WalMart and other discount stores than it is to buy fabric and make one. The advantage to sewing your own is that your choices of fabrics are so endless and it will be higher quality. Since you already have the fabric, it will definitely be better for you to make one.
Good luck with your project and keep us posted (hint,hint pictures!) on how you make out.