Don't laugh:
I consider one of my most important tools for my pool to be a full-length wet-suit, with boots, gloves and a hood. When you have a leak and the water is 58 degrees, it's the only way you can fix the leak under water safely--you can actually WORK in the water. A full length wet suit can be as little as $100 from West Marine--it doesn't have to be expedition quality.

There ARE underwater patch kits--they are a pain to use but they work. I find it helps to have a little rolller like the tile guys use. Plan on AT LEAST 2 layers--a first patch over the hole, then a much larger patch to cover, protect, and seal the first patch better. Bad holes can require 4.

Look around your pool for signs of leakage--a tell-tale trail of sand is a good one for example. This narrows your search for the hole enormously.

Good luck!