Although not always checked, the yellow fever vaccination has been a requirement for some time for travelers entering CR from Colombia (and Peru, as well). It's not required for travel between Colombia and the U.S.
Get your shot at Clinica Biblica or CIMA. Make sure you let them know you need it for travel to Colombia. They will give you documentation that you need to take to the Ministerio de Salud. You will then fill out some papers with them and approximately a month later you will get the World Health Organization card that you need to travel. Stupidly, it didn't dawn on me that it would take a month for them to process something that should take five minutes. As a result, I had to reschedule my first visit to MDE. When I finally made the trip, Copa did check my documentation before letting me board. I've heard that they don't always do this even though it's required.
So the bottom line is that you should start the process a couple months before your planned travel.
