Most upholstery shops have different size round foam on a roll and sew it up as needed out of the material used in the car. The Wizzard
SMS Auto Fabrics in Oregon and Original Auto Interiors in Michigan. Both have a website. Just do a google search.
Cheapest I've found, $3.30 a yard! http://www.perfectfit.com/15976/154170/Weatherstrip--Trims/Windlace--Automotive-Cloth-Covered.html
x2 The roll I got for my Chrysler looks good except for one fugly seam where they joined the fabric together that I have to deal with. It's about a third of the way through the roll.