Follow-Up:
Someone on the Rialta Yahoo Group has said that www.busdepot.com has A/C compressors for the earlier 5 cyclinder Rialtas in the $300-400 range. That's actually a very good, and I wish they also offered VR-6 compressors, but they don't. Chris www.MotorHomepage.com 2000 Rialta QD
Here is a link that might be useful: MotorHomepage's Rialta Resource