Dave, you might try contacting the Alamo Defenders Descendents Association (http://www.alamodescendants.org/) or the Daughters of the Republic of Texas (http://drt-inc.org/). Another Scot, John McGregor, is better known. Defenders listed as from Kentucky, Tennessee, and points south are most likely of protestant Scots/Irish descent, some of them perhaps born in the old country.
- Phil

Here's a couple bits from the indespensable Handbook of Texas Online.(http://www.tshaonline.org/handbook/online/articles/BB/fbadt.html)

BALLENTINE, RICHARD W. (1814-1836). Richard W. Ballentine, Alamo defender, was born in Scotland in 1814. He traveled to Texas from Alabama aboard the Santiago and disembarked on December 9, 1835. He and the other passengers signed a statement declaring, "we have left every endearment at our respective places of abode in the United States of America, to maintain and defend our brethren, at the peril of our lives, liberties and fortunes." Ballentine died in the battle of the Alamoqv on March 6, 1836.
BIBLIOGRAPHY: Daughters of the American Revolution, The Alamo Heroes and Their Revolutionary Ancestors (San Antonio, 1976). Bill Groneman, Alamo Defenders (Austin: Eakin, 1990). John H. Jenkins, ed., The Papers of the Texas Revolution, 1835-1836 (10 vols., Austin: Presidial Press, 1973).
Bill Groneman

MCGREGOR, JOHN (1808–1836). John McGregor, bagpiper and Alamo defender, was born in Scotland in 1808. McGregor lived in early 1836 in Nacogdoches. He took part in the siege of Bexar and later served in the Alamo garrison as a second sergeant of Capt. William R. Carey'sqv artillery company. It is said that during the siege of the Alamo, he engaged in musical duels with David Crockett,qv McGregor playing the bagpipes and Crockett the fiddle. McGregor died in the battle of the Alamo on March 6, 1836.
BIBLIOGRAPHY: Daughters of the American Revolution, The Alamo Heroes and Their Revolutionary Ancestors (San Antonio, 1976). Daughters of the Republic of Texas, Muster Rolls of the Texas Revolution (Austin, 1986). Bill Groneman, Alamo Defenders (Austin: Eakin, 1990).
Bill Groneman