Need Belt Pulley, Help

I use my 87 Astro for alot off offroad use, it's equiped with the Overland Vans 6" lift kit and 30x9.50 tires ( http://www.overlandvans.com/ ). One day I got the notion to install a winch and wanted to use a separate alternator and battery setup to power it. I found that with a little cutting on the bushing pin that a second alternator lined up and fit snuggly into the A.I.R. bracket, like it was almost made for it.

My problem is the my van didn't come with the little idler pulley for the A.I.R. pump (the one that sits between the A.I.R. pump and the A/C compressor). I purchased a junk van a few years ago as a parts donor, but it didn't come equiped with A.I.R. either.

If anyone could please help me find this part, or a good alternative, I would greatly appreciate it. I have a 87 astro 4.3l with AC, everything is in it's factory location, except the second alternator mounted into the A.I.R. Pump bracket. Thanks