I nearly got arrested once for ordering a custom
gobo that had a swastika in the centre and the words "Arbeit Macht Frei" curving around the symbol. It was for a production of "Playing for Time" by Arthur Miller.
We here can get what are called cabbage crates. They are a lot flimsier than most timber but stronger than Balsa. I have no idea what timber they are made from but it is very soft breaks easily but doesn't splinter. I will try and find out what the wood is.