Unfortunately, you are using an out of date browser which is not fully compatible. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
Since this is a specialty product and is cell cast, it is not always widely available. At times it is necessary to buy several sheet, to get any. Check with your supplier and see when or whether they order it.
My first question is...do you really need 1/4"? You can get 3/16" UV acrylic in 48 x 96 and 72 x 96 and would only have to purchase a sheet at a time. As far as I am concerned most of the time the extra 1/16" of thickness only adds weight and is not necessary. Before you decide to purchase 1/4" check the prices and availability of 3/16" material.
We bought some recently for a commercail job using stand off hardware. It had to be that thick because it was large. We drew out the specs and ordered it from a local supplier. I'm sure they ship. I'll look it up and PM you.