Don't know where to find one exactly. But you have some alternatives:
1. Have the sleeve shortened (cost about $25)
2. Roll the sleeve up if it has a nice lining.
I purchased this one from Target and had the sleeve shortened:
http://www.target.com/p/mossimo-womens-trs-boyfriend-jacket-black/-/A-12411226
I am wearing this one more often than my other expensive blazers, haha.
