If you have the manual and the proper commands, you can write the driver yourself. It just becomes a matter of creating a VI that sends those commands. Your task is much easier if you can copy and modify an existing VI that already communicates with your instrument. This technique, however, will not work for VIs with library nodes. In this case, you will have to write the LV code from scratch. Look for a legacy driver on our insturment database for some examples.
Jeremy Braden
National Insturments