Gareth -

Captain Barlow's Company is not separated out in the Waterloo Medal Roll. However, he and many subalterns are listed in the WRoll.

Have you checked the following article? Unlike the Waterloo Medal Roll, it does list his company and all the enlisted soldiers in it, but not the subaltern.

http://www.napoleon-series.org/military/organization/Britain/Infantry/c_2-69Waterloo.html

I find it interesting that the company muster rolls did not show the subalterns. You can contact the author by clicking on his name on the article.

Good luck!

Bob