ebay works well for buying techni ice. We are going carryon only on Saturday. I do like having the techni-ice for the beach, I may bring a couple of sheets that I haven't activated yet. It's so much lighter than ice!!
I've bought it twice...once on eBay and once on Amazon.com.
I would think that any sporting goods store worth it's salt would carry it. However, it's an Australian product, so that may be why it's harder to find in a retail store.