I suggest getting his obituary. If you're lucky it will list the town he was born in. I also suggest checking with the church he was a member of. Again if you're lucky his burial record will list the town he was born in.
Occasionally the death certificate or marriage record of a child lists exactly where the father was born. It's a long shot but might be worth trying.
Your last option is to look for his birth record through the civil records for Alsace one town at a time. To say the least, even though the records are online, it would take you a fair amount of time unless you get lucky. The records for Lower Alsace are at the Bas-Rhin Archives website. The records for Upper Alsace are at the Haut-Rhin Archives website.