Where can I find a reasonable NLP CFG or CSG for English?
It is uncommon to use a "closed set" context free grammar because the number of production rules is staggeringly large. The typical approach is to recover a probabilistic context free grammar from a treebank (e.g., the Penn Treebank) in order to do statistical parsing (via probabilistic CKY, Earley, etc).

The only time you might want a "closed set" is when working with toy data in which case you may define an overly simplistic subset of English grammar dealing with sentences, noun phrases, verb phrases, and so on. Such miniature grammars can be found in standard NLP texts such as Jurafsky and Martin, and Manning and Schuetz.