Brewer (who is owned by Bernina) makes a "Bernina compatible" bobbin, and that's all I order for the store. The part number is 0115367T. They retail for about $1.25 each.
The Bernina bobbins have a slightly tighter center hole than the Singer 15 class bobbins. They have the gnurling on the shaft, and the top and bottom are smoother. I wouldn't mind shipping you some. I'll send you a private email.