A few suggestions that may or may not be helpful:
I find the lighting has a lot to do with my panic attacks. If your office, like many, has not-so-great lighting it might be helpful for you to have lamp (if that is possible) at your desk.
Lavender hand/body lotion. It's very calming.
Stretching has always helped me with my anxiety, so has coloring (in a coloring book...which I wouldn't do at work but it is very relaxing!).
You seem to know when you are most likely to get panic attacks, try and figure out if it's a specific time of day or specific situation that triggers the attack. If it's something you can change, change it. If not, you can prepare yourself and try and lessen the attack.