Littonware microwave dishes are available online from eBay and Amazon.com, as of 2015. There are a number of options available from the Littonware line, including casserole dishes and bundt cake pans.
The selection on Amazon.com isn't as large as the one on eBay, but there are a couple of options including the 8-piece set. This set includes a Dutch oven and casserole dishes of various sizes. On eBay, there are more options, including the ability to purchase the 8-piece set. There are also sellers who have individual pieces available. Littonware dishes are not only compatible with the microwave, but also usable in convection and conventional ovens.