They’re still made and still legal, though because the demand isn’t that high they don’t make a huge quantity. You can get some from your bank upon request, though if they don’t have any on hand you may need to wait for them to get some on your behalf. The main thing needed for $2 bills is popularizing them.

$1 and $2 coins would also be a good idea, honestly, entirely replacing the corresponding bills, like Canada and the eurozone have done, and also eliminating physical pennies like Canada and certain euro countries. But those are harder fights. ($1 coins do already exist, in small quantities, alongside the $1 bill.)