RioRico has found some bargains.
It looks like around $40 delivered is ebay's going price for PK/A teleconverters - there are a few Takumar-A teleconverters being sold now and the bids are currently low.
See:
takumar-A teleconverter | eBay
What is it that you are trying to do?
If all you want to do is to make p-ttl flash work while you use a manual lens then all you need do is to fool the camera into thinking an A type lens is mounted. There are a few ways to do that, one of which involves removing glass from a TC and another makes a minor, easily reversible change to the camera's lens mount to make the camera think that all lenses are A type lenses.
If you want to use a no-aperture ring lens and set the f-stop using the camera's e-wheel then you'll need true A type tubes. Two PK/A teleconverters at $40 each isn't much to pay for A type extension tubes and in my experience removing the TC's lens stack is easy and reversible.