Self Leveling Control Unit

I had found a website about a month or so ago that sold this unit for around $120 but I wasn't prepared to buy it at the time I saw it. Thought I had bookmarked it but to no avail. Does anyone know where to buy this module (other than at the dealer)? I can't seem to find it again on the internet. I have a 1999 Montana with the rear self leveling suspension and I am sure this unit is not functioning properly (will not cause shocks to deflate, inflates - yes, deflates - no). Thanks.

I saw a unit for sale on ebay last week...

GMPartsDirect.com or RockAuto would be the first two places I'd look.