Boba Maker has the smoked acrylic. I hear they are the best.
There is one on Ebay, but I have broken all three of the ones I bought in the same spots. Quality wise, They look great, but I just sucked at putting them in a bucket.
You can get the dark green one, which I use, from either RJsafety.com, but they are backordered. If you need one quick and cheap, the same that RJ sells, go to :
http://www.school-safety.net/4118-DRK-SM||Eye_Protection||Headgear_and_Faceshields||Faceshield_Only_-_Dark_Green_Faceshield||4118-CLR-SM,4118-DRK-SM.htm
I just bought three of them. Works perfectly.