Well, I'm sad to say that Seattle Pottery Supply doesn't have any Frost at the moment, and Claudia who works there said she wasn't sure if they were temporarily out of it or if they're not going to stock it anymore. I broke down and bought one bag of Cool Ice, but man oh man I hope I don't like it. It's over 5 times as expensive as my usual porcelain!
I was there right before closing and they were really busy. I asked if they had Joe Finch's book of kiln construction, but they didn't know offhand and didn't have time to check. Sorry!
I think you will be disappointed in Cool Ice. It is Southern Ice formulated for cone 6 but it is not as translucent as Frost. Seattle Pottery Supply is one of the best stocked ceramic supply stores in the country. I even have to sometimes order from them even though shipping from WA to GA is a killer because no one else has what I'm looking for. Unless Laguna stops making Frost, I find it hard to believe SPS plans to stop stocking it. The cone 6 porcelain you use (I forget the name) is the only clay I know of that looks like from the pictures you've posted to be as translucent (or maybe even more translucent--which will turn my world upside down!) as Frost.
Jim was correct about my disappointment with Cool Ice. I haven't been back to SPS yet to see if they have Frost back in stock, as I just finally got around to testing the Cool Ice, and got a couple pieces out of the kiln last weekend. Here's a photo of two tumblers, NZ6 on the left and Cool Ice on the right. They're the same thickness, and they're side by side in the same amount of sun, I swear. The difference is stunning.