I agree with Joe, Sew Classics has given us very good service, ships fast and takes Pay Pal. We order all our parts from them. I use both plastic and steel bobbins without issue. The plastic ones are quieter and won't wear as much.
I learned to sew with the steel ones back in the 60s. 66 bobbins are the most common ones and can be found locally. Don't forget to oil your machine and change the grease, if it has hardened inside the machine. It will last a lot longer. We're all they have, so be good to them. You will be collecting vintage machines in no time. It is addective.