The post offices here in Irving TX are doing away with their single stamp overnuight vending machines, so you either have to buy a bopok or wait in line during the day. That irritates me greatly. I wonder how widespread it is.
Our town of just under 6000 got rid of the stamp dispensing machines around 2002 or so. The advantage, and it took some adjusting to- is we can and do buy postage stamps at the grocery stores while shopping. Of course we can still get out of the car, walk up the mandatory steps (beautiful old building built back in the 1930s or so-)and stand in line. The plus side is our postal people are for the most part outstanding.
Unlike when my son was in Guatamala. You mailed nothing beyond letters because the postmster kept any and all packages. You could have it if you were willing to pay enough and if the postmaster did not want it worse than you did.
Go to usps.com and order stamps online. USPS will deliver your stamps to your door, with delivery confirmation