where to find my Altera ID?

It sounded like you ran into the same problem I had when we received our renewal package. Nobody bothered to register our NIOS development kits so when it was time for the renewal registration we didn't have MAC addresses assigned to an Altera ID for each NIOS II shipped.

If this is your first time trying to register the kit (I'm assuming this is the reason why you wanted your ID number) and it doesn't seem to let you I would contact Altera about that.