repotting small oncidium

[guppylove1985]

Hi, I have a small oncidium 'sharry baby' that I bought as a division from an orchid show. It was doing great for the longest time but with the incredibly hot weather we've been having, I'm having a difficult time keeping it wet enough. It is potted in a very well drained mix that looks to be mostly rock and perlite. Now the leaves are showing dry, brown ends with black spotting, and I'm sure it's because it needs more water. I already keep it sitting in a saucer of water, but i'm wondering if I should repot it in a different orchid mix that will hold more moisture. Does anyone have any tips?

thanks.
here are some pics.