you have the right crossbars. just hit the local pick a part junk yard. look for anything with a similar style crossbar. i just unscrewed the roof rails, and took off the part that slides down the channel. i think i got some off a blazer for my rodeo a couple years ago. perfect for about 5 bucks. and yea, if you want the part from the dealer, you have to buy the whole thing, roof rails and crossbars to boot. this was discussed about a year ago or so...

'99 Trooper, 912's
'89 Trooper RS, 2.6