There was a Dr H A Swan in Abeline Texas from around 1919 to 1945 (he died in 1945). He was a medical doctor. Here is a (small) advertisement for him
https://texashistory.unt.edu/ark:/67531/metapth91295/m1/4/?q="dr%20h%20a%20swan" Could not find any plausible HA Swans in IA, or even any H Swans that were doctors. If they sold nation-wide then maybe they did sell to the doctor in Abilene. Coincidently, my great-grandfather had a farm near Abeline that same time frame.
A free research site is familysearch.org. It is ran by Mormons, but you do not have to be a member of that church to use it, and you do not have to give them any information either just to go there and do some research. They have Dr H A Swan's census records, WWII draft card, death certificate, etc.