I bought some at a local shop that just sells dash covers, floor mats, and seat covers. They fit my high back 60/40 perfectly. I think they were around $50 or so. Call around town and see what you can get.
x2 - ebay ones are good. I bought a pair and they fit snug. They even have a built-in pouch for storage behind the seats. Don't over tighten the straps though cause it'll rip right where the seam \ stitch is at.