Well, for my GameBoy advance SP I went to radio shack and bought gba/gbasp protective plastic sheet things, and you can cut them out to the desired shape for either your gba or sp, so i'm guessing you can also cut out a peice small enough for your tama's screen.
ok, first of all I´m colombian so don´t judge my english... hehehe I´ll try to do the best I can...
I´ve heard or read in another forum of the same problem, and that member stuck on th screen a transparent paper, I know the name in spanish hehehe, well it´s like this, its kinda shiny on one side (not too shiny) and the other side is sticky, so you just have to cut an exact piece of that paper and stick it on the screen, this will avoid scratches on it, but you have to cut the exact pice cause if you cut sameller than the screen then dust and dirt will get in the edges where there isn´t that transparent paper and that´s really tough to clean... hope you understood and was of help