Thanks for reaching out. I'm new here too, and don't have any particular knowledge about bipolar disorder or networking groups, but I'm sure someone here might.
One thing I would say, though, as someone who experiences some social anxiety and social isolation myself, is that it is probably best to be conservative when introducing the idea of group sessions to your partner. For some people, particularly those of us who experience social anxiety, the very idea of groups of people can be enough to inspire terror and could cause more distress. I'm not saying that is necessarily the case with your partner, and I'm also not saying that group sessions can't be helpful, I would just suggest playing it carefully particularly when he is already grappling with a new diagnosis. Be gentle to start with :)
I do know, however, that there are carer's groups around, so that could also be an option for you if your partner is not quite ready for a group setting himself. It's great and wonderful that you want to look after him, but you have to look after yourself too, and it may give you some of those ideas that you are looking for.
Best wishes, and good luck,