From a quick peek in Google you can learn that underwater nudity is not that rare, if you wish to find these pictures you must first use all your low tech options.
What else do you know about the model, the photographer, the equipment use etc?
My guess you should check in Sharem el Sheik it self for old people who might remember any tourists going under the water with a camera – there could not have been to many of them.
Another option is to contact old photographers who use to hang out in these areas or did any nudity pictures at the time. For that you may find many Israeli photography forums and nudity enthusiasts’ forum.
Good luck