Welcome to the forums and thanks for reaching out and being here. A big credit to you for wanting to help your partner and being so supportive with his anxiety.
I think the best thing that you can do and that you've done is to try and get him back into see a psych. This is really the best option since they can work with his anxiety individually and give him lots of tools in working around it. It sounds like he is quite motivated to change.
Can you tell me what happens when he has a panic attack? How do you both cope in that moment? Little things like working through breathing techniques can be incredibly powerful or types of affirmations "take a deep breath in with me", "it's okay" and "you're safe" might be helpful to hear.
I think the other thing that might be important is to talk about the placement. I imagine the worst case scenario might be that he has a panic attack at work, but if that were to happen - it would be totally okay. Nurses are all too familiar with panic attacks, and being a placement; they can give him that extra support and try and accommodate his needs where possible. If he is able to talk to the placement coordinator it could make a big step in knowing that he's safe and supported should anything happen.
The last bit of advice I can really give is to talk to him. Everyone is a little bit different in how they experience anxiety. Asking questions about 'how can I help?' 'what do you need me to do in those moments?' might be helpful.
Hope this helps,