I ordered mine from Uni-Grip in Upper Sandusky, Ohio. It's sold by the foot and I ordered 30 ft. and I believe it cost about $4 a foot plus shipping. I was able to discover the Uni-Grip part number for mine by noticing Uni-Grip's number in an email response I received from a Monaco dealer after I sent them a request for prices. I don't know if Uni-Grip can tell you the part number you need but if push comes to shove; you could probably cut a small sample from your old one and send it to them and they should be able to match it. As you can see from their catalog; there are many options that are very similar!! Good luck and let me know if I can help further.
Here is the link to their website: http://www.uni-grip.com/dealer_catalog.pdf