There is one free corpus of business English at the Virtual language centre, Hong Kong Polytechnic University. http://vlc.polyu.edu.hk/concordance/WWWConcappE.htm
You may choose it by clicking "select a corpus". But there's little information about the composition of the corpus except some brief remarks like
"Business & economy Texts on business & economics, compiled from internet documents, 1998. 119,972 738 kb ".
In that case, it may only serve the teaching purpose.