Does anyone know where you can get those little ice packs that slide into your nickers?

I have bad swelling, which I have been assured is just from the extra pressure and blood flow made worse by my sacroillic joint dysfunction, but after a day of being active and on my feet is can be really painful and uncomfortable.

I was given frozen condoms by my hosp for the swelling after the birth of my first, but I wanted something a little more re-usuable and economical.

Any one know?