Earlier I showed a neat resource that has grammatical and ungrammatical sentences from various linguistics papers over the years. But what if you want a whole bunch of English errors?
In that case, check out work that David Hale and Adam Kilgarriff are putting together: http://clt.mq.edu.au/research/projects/hoo/.
You might also look around for ESL corpora, for example:
- CK Jung’s lab has a one-million word written corpus of Korean learners of English (“YELC”): http://www.uclouvain.be/en-cecl-lcworld.html.
- Izumia, Uchimotoa, and Isaharaa (2004) have a Japanese Learner English Corpus, too (NICT JLE), but I think you have to email them.