Duncan Alexander McCallum is very easy to find. He is on Rootsweb, Genforum and Ancestry. Everyone seems to know he was born in 1832 but no one has posted the month and date.

If you have not done so already, you should post a query on Genforum because by now someone may have discovered a birth date and not posted it. You can also contact the people on Rootsweb. These are free sites.

Also, how about a pension record his wife may have filed or the indigent soldier's records. These may not have any information you don't already have but leave no stone unturned.

Sorry I could not find it.