MOst paint stores carry universal tints (able to be used in oil or latex). The most popular brand is Caltint, which is what we use. The downside is that they range from $9.00 to $14.00 a bottle. Reds are usually more expensive. It takes a lot of red to make it hot pink, but a bottle will usually do it, just get the primary red (I think it's called medium red), not the venetian red which will turn it a muddy color. Add a little at a time until you're happy.
One other note, keep a piece of paper nearby and put a splotch on it from time to time- dry it quickly with a hair dryer to get a true read, it's be darker than what you see in the can...