I was able to junk yard an idler like this :
idler pulley. Came from a Nissan Maxima IIRC but it doesn't matter really. Just something like that, add some washers to stack it off the block, and ignore the V-configuration. It's just enough to take out the vibration, there's really no pressure on it. BTW I'm not saying this pulley will work, just one like it. Maybe I can grab some measurements later.
I think I did that 10 years ago? Maybe longer. Haven't lost an alternator belt since. And because it's "taller" than the v-belt pulley, it still touches the belt using the existing lower bolt for the alternator adjustment bracket.
Sorry I'm late to the party!