I have not seen any evidence that the fertlizer for the OKC bombing was manufactered in West, TX. The fertilizer was purchased in McPherson, KS. that doesn't mean it wasn't manufactured in West, but there are fertilizer manufacturers and warehouses in Kansas and Missouri, so it would be unlikely that the fertilizer for the OKC bombing came from West, TX.
(41) 50 pound bags of fertilizer were purchased from Mid-Kansas Coop in McPherson, KS. McVeigh started planning the bombing from his home in Herrington, KS before he moved the operation to OKC.
Also, fertilizer was not the only explosive ingredient in the bombs. some of the barrels had both fertilizer and nitromethane and some had deisel fuel.
http://en.wikipedia.org/wiki/Oklahoma_City_bombing and coincidentally (?) today is the 18th anniversary of the OKC bombing (April 19, 1995)