The last time I went to Ollie's, they were still there in a variety of colors at $4.99. They are about $17 on Amazon; I got my blue kit sometime last year and just finished painting my calipers, this afternoon. The brush that came with the kit was useless. I used cheap 1 inch natural bristle "swarf" brushes from Harbor Freight and some solder brushes for the tight spots. You need at least one of each brush for each wheel. The paint dries very fast and clogs the brush. The will become throw a-ways. My car is only 18 months old, so there was NO corrosion. I took four hours, but the calipers look great.
I used the 2 parts epoxy paint above. My friend used the aerosol one and after a few months, the color changed and turned dark! To use this 2 parts epoxy self leveling brush on, you have to plan well ahead because once you mix them, you have about 2 hours. I had to do this by myself, so I invested in the electronic jack to help speed up the lift which worked out great. You need to do the prep work very well and the kit comes with a can of brake cleaner. The hardest step was to paint the inside of the calipers but of course no one will see if you messed up
I recently went back to Ollie's. The price of the kit is $2.99, not $4.99. And, they still have them in stock.
Be sure to get some of these brushes from Harbor Freight. Pack of 36 1" Industrial Grade Chip Brushes They have many uses. Because the paint dries so fast, you will need at least one brush for each wheel.
Does painting the calipers void any warranties? I have 11K miles on my 2013 and I don't want to do anything that might disqualify me from a warranty.
No, unless Toyota can prove that it cause the failure. That's pretty remote, although you can claim anything. It's like being sued. There is no "bottom threshold."