now the question is - What are the bores like - Much pitting?
have it checked by someone who knows vintage double to make sure its in safe condition and then get some RST shells for it
http://www.rstshells.com/
if you let the members know where you are we might be able to recommend some one near you
but - a graded 0 frame 20ga
i hope where ever you are its upland bird country -