Sentgen -- "Sentence Generator"
This program is completely free. However, if you use it in your research, I ask kindly that you simply cite:
Dale, R. (2007). Random sentences from a generalized phrase-structure grammar interpreter. arXiv: cs.CL/0702081. [link]
"Sentgen" -- "sentence generator" -- is a little C program that takes as input a phrase-structure grammar file and constructs example sentences based on that grammar. There are a number of options in sentgen, including output to human readable files and TLearn file generation.
To compile: cc -lm sentgen.c -o sentgen
See a brief instructions page for sentgen.
Get the sentgen .tar file (with sentgen.c, and some sample grammars).