Glad your arm is better! Sew-classic has bobbin tires. You could email her and ask which size for the 128. It might be the standard size.
http://shop.sew-classic.com/Bobbin-W...-Tires_c16.htm
Is the old tire stuck and not wanting to come off? I haven't had this problem so I don't know what you should do. But it looks like it might be easier to work on with the handwheel off. (I know, you already did that!) Maybe you could soften it up with something that won't harm the machine, like oil or even liquid wrench? You'll then have to get all the oil off the wheel before you put the new one on.