Idler pulley alternates are available at any auto parts store, under designations for different cars. You have to pur research in to find the right size, bearing, etc etc but I've done it... I dont have any of the info anymore though and my head hurts just thinking about researching again. Basically you mean need a 90mm pulley with a 17mm bore, and at least 30mm width.

But aaannyywwwaayyys, I have a ringing from my engine bay also. Sounds like a pulley. But both my idler pulleys are good, dead silent and spin solid. In fact I've replaced one for other reasons so that leaves only 1 other old one, but its good.

So I hope they were right when they diagnosed your idler pulley as being the problem....