There are other questions here enquiring about disabling FireWire ports reversibly via software or irreversibly via hardware (e.g. epoxy/desoldering).
At a cleared defense contractor we actually looked at building these and it is not that hard of an issue. Not foolproof, but fairly reasonable. It was a cyber-security research program and it did not get funding, but I always thought it would be a great commercial idea. At the time (a couple of years ago), to my knowledge, no one was doing this for firewire. Not many for USB, but it looks like the USB market has changed.