Honestly, I've never seen platic egg crate ANYWHERE. I've only ever seen it online. Before looking into false bottoms some time ago I didn't even know it existed or what it was. Maybe someone else will know where to find it. I worry about the gravel, though, as it is very heavy. It'll probably be fine, but that thin glass makes me worry. LECA/hydroballs are another option, but is probably too expensive and can also be difficult to find in retail, unless you have a good reptile/vivarium supply in your area. Personally I made a small leap of faith and bought ODLA clay pellets from IKEA, as they seem to be normal clay with no additives, and they wouldn't be in direct contact with frogs anyway. They are around 6$ for 4.5 quarts. I found a post on Dendroboard by someone stating they used it, so I decided to try it, but I feel it would be irresponsible of me to recommend them before having used them for a while.