If you're talking about the CSX OEM spoiler then why not just get the Aspec TSX one? They look quite similar and have the same height. The CSX has the same dimensions as the 8th gen Civic and the trunk is different from the one our TSX has so you probably have to investigate the bolt patterns in addition to length.
However since the CSX is an 8th gen Civic, the real question is whether an Si sedan spoiler would fit since it's arguably more common and likely to have been tried.
A new CSX spoiler can turn your car into a boring, everyday driver to a track monster. The looks and style of our CSX spoiler options are designed to flow with the body lines on your car, not take away from it. Low, low prices make these a great choice for anyone.