Since I can't get it refilled, does anyone have a suggestion of a good Tulsa local place to have it removed so I can retrofit?

 

R-12 is a pure refrigerant meaning it's not a blend of two or more individual refrigerants which means that you certainly can find Freeze-12, a drop in replacement, for your R-12 mvac. In other words all is not lost if you are not changing your system entirely over to 134-A and simply want to add some refrigerant.

Google search "R-12 drop in replacement" and you'll find a lot of info. Pay attention to what all is recommended be done. Many times a flush is required yet many people have experienced zero consequences without one, simply adding a drop in to the system.

 

Mainstream Engineering Section 609 Manual

R-417A is a direct drop in replacement, compatible with ALL refrigerant oils and that's what counts.
Refrigeration & Air Conditioning Technology - William C. Whitman, William M. Johnson, John Tomczyk - Google Books