Call your former boss to ask whether he is hiring or whether he

 as you're looking for a new job. The most probably he will ask why and you could hint that your new boss give you poor review. I don't think a lot of people would like to get too much involved when you're fighting with your current boss. It's a shitty situation and people tend to stay away from it. And I don't think it's a wise idea to send an email to a group of people to vent what you're suffering.