There are muster rolls - where are they? It depends, of course, which regiment your relatives served in, and the fate of those regiments. If you know their regiments, and if you know what happened to the regiments in all the various amalgamations, etc, then it's worth approaching the modern regiment and asking if they have muster rolls in their archives, or where they might be - or you could try the National Army Museum in London which might be able to tell you. Sorry - I'm not being much use here, but I don't need to look at muster rolls to write the Sharpe books so I've never gone searching for them. If all else fails then a genealogical website might have clues to this?