I think I see them at RockAuto dot com
for $25-$60 at rockauto, though I'm having a little trouble interpreting which part on the list is exactly the right one.
I'm having nightmares with my '02 Silhouette AC right now... one small garage didn't want to deal with it, and the dealer wants to replace the rear AC lines for $1600! (Got a kid in private University ... can't do it!) And they charged $200 to diagnose it.
Same symptoms ... the rear has blown hot heat since we bought the van used 2 years ago. That was probably the expansion valve (I hope not the rear condensor). But now there's a rear line leak so the front AC doesn't work either.