JP, a frequent commenter on this blog provided the contact details for a compay that provides a basic defensive driving course. See below. I've copied his comment here so more people see it and read it.
SCS (Safety Cooperation Services Co. Ltd.) corporate training centre located at LANSAB which is adjacent to Ghala (Tel: 24585294; Fax: 24586068; Contact: Mohammed Salim). Course costs ONLY OR 21.-, 3 hours class, 5 hours on road. Tell them ahead of time if you need an automatic transmission.
Also other Oman training organisations provide similar courses: OTI, NTI, STS and TATI.
I, (suburban) would like to add that I've taken two defensive driving courses from the company called OTI, Occupational Training Institute, I thought they were great. I would provide the number, but my phone book bit the dust in the recent flood.