Hi, Sylvia!
Well, there are several approaches you can use to get a strobe. However, all of them, in general will require that you get a "tray" with which to mount it to the camera and some "arms" which attach the tray to the strobe.
Nikon made great strobes and included the tray and arm with the strobe. You can still find them new at a variety of camera shops on line. For example:
http://www.bergerbrothers.com
Sea & Sea make nice strobes and you can view their wares here:
http://www.seaandsea.com/
Ikelite makes good strobes, too:
http://Ikelite.com
Sea & Sea also make trays for the Nikonos as you see on their website. In addition, a very fine company, called Ultralite make excellent trays, arms, etc. for the Nikonos:
http://www.ulcs.com/
The bad news is that you are looking at a ca. $500-$1000+ investment. However, for u/w photos of high quality, it is a "mandatory" investment. I have successfully purchased items on eBay, but I always have them checked out by my phototech> I can make some recommendations for phototechs, but they will require that you mail you purchases to them--sort of a pain!
Use of B&W film does not solve the light problem, but it does provide a certain "atmosphere". In particular, the graininess does not seem as bothersome with B&W enlargements--it makes for a mood. Jim Church, among others, has done some wonderful B&W work on wrecks. His ex-wife, Cathy, has also made some fantastic high contrast photos in B&W. If you have a darkroom at your disposal, it might be fun to give it a shot.
Hope this helps,
Scorpionfish