Search Amazon for beer bag, beer cooler, can cooler, etc. They have lots of choices and you can look at likely suspects to see the measurements. I use a six-can bag for 4x5 film holders, for instance. Here's something too big, but it's the kind of thing you can find there: https://www.amazon.com/Polar-Bear-Co...dp/B00259FY1Y/ It's the wrong size, and too expensive, but just one of many, many possibilities.

Here's a nice one, cheap, just a bit big: https://www.amazon.com/dp/B006HFBNYO/