What bus are you looking for? What size do you need it to be?
I've seen PC104 cards, PCI cards, and PCI express cards. I haven't seen anything specifically intended for small chassis, but there might be one that happens to work for you.
Dear Jesper, thank you for the feedback. The profibus network is already there. It is rather old setup. I'm just replacing failed computer with anther one. The rest of the system is not changed. We already have one spare Business workstation, so I thought it would be a good idea to use it. I need profibus card that will fit SFF casing. Also DP/USB adapter cannwork but I'm not suremif this can be a long term solution.