New replacement bobbins on ebay and various places are generally good, but (!), if your 115 is anything like my old 99 and 201 there are problems with uneven quality. Of 12 bobbins I bought, I kept 6, the rest would not go on the bobbin winder. They were too coarsly finished off inside the "hub" and I just had to buy another bunch and see how many usable bobbins I end up with. This problem hardly exist on vintage bobbins.
Thanks for the links, they are always useful. There are some places that bothers with used and vintage parts, they have been life savers some times.
Which parts are you looking for?