heated pet bowl help

Can someone please help me find a 1 quart heeated pet bowl. Im only finding the 5 quart or bigger. I need the smaller one because there are 2 cats outside that come to my house from time to time and I want them to have water for the winter.

So if you could help that would be great!

Sorry its not horse related.

My barn cats will climb the side of my horse tank (about 3') and balance on the lip to get a drink
If your having a hard time finding something small, you can get a chicken water heater that is just a flat thing that the water bowl sits on. They sell them at most feed/supply stores and they run in the $30 range.
ETA- have you looked at bird bath heaters? That might work too. Either way you can use whatever size bowl you want.

I've had the same problem. My one outdoor cat can crawl into the bigger heated bucket, but the tiny outdoor cat (seriously, 3 pounds, full grown!) can't and she doesn't ever leave the barn anyway. So I thought about getting a small fish aquarium heater and putting it in a small bucket or bowl for her in the barn. I have an unused bird bath heater though, I might as well try that first. But you might find a very small fish tank heater cheaper.

Thank you everyone for your help... I just ordered one on amazon. I hope the cats will like it. :)