I would check Craigslist first...here are some I found in MN, but you will have to determine if they will fit your truck (most don't list size or vehicle it came off of in the ad)
http://minneapolis.craigslist.org/pts/370719279.html
http://minneapolis.craigslist.org/pts/360239592.html
http://minneapolis.craigslist.org/pts/359729863.html
http://minneapolis.craigslist.org/pts/359290576.html
http://minneapolis.craigslist.org/pts/344305150.html
http://minneapolis.craigslist.org/pts/344017405.html
There is a truck and van shop near me (in Ham Lake), called RADCO, you could try contacting them. They sell all sorts of stuff, including toppers.