Rear Brake questions - 79' KZ650

Well, my rear brake is a bit useless at the moment.. It works but not all that well, tons of movement and no were near getting it to lock.

I bled it and replaced the the pads and that only helped the situation marginally so now I am down to 2 things to firm it up.

1.Shims- when I replaced the pads yesterday after removing the cobwebs I discovered there are no shims. Were can I get these or can I make them up myself? I went to the local salvage yard and the only set I could find were rusted to non functional status.

2. Rear Master cylinder rebuild- Were can I obtain a kit for this? I checked Z1 but they do not have one specifically listed for my bike. I have had little luck googling one up as well. Is there an alternative model/year that will fit the bill?

id flush out all the brake fluid and keep bleeding them,see if that helps