Thank you everyone for the input! I was not planning on using plastic, as it just does not seem right to use plastic on such lovely old machines.
I looked on ebay, but couldn't find any nice old ones. I'll just have to keep looking, or try some from JoAnn.
I don't want to have to end up winding the bobbins by hand, so I'm definitely leaning toward buying old bobbins.
Thanks!