They are ordered from the manufacturer (idemia,thales/gemalto,oberture) with speficied memory size depending on what capabilities are needed.

The big iffy is that manufacturers were compromised (by the US afaik) in 2015 and all cards from then or earlier should be considered compromised.

Few carriers encrypted their OTA-keys before then. I know that some carriers did not send encrypted keys to manufacturers still in 2018.