It has been a struggle to find 18-24 month old boy undershirts--the plain whit T kind that daddy wears. So, after many trips to Target, Walmart, etc., my MIL got tired of helping me look and finally ordered them directly from the Hanes website. I can't tell if you have to buy them individually or if it's a package, but they have them. (they also have them in 6 & 12 months).
Hanes