I do not have the manual or spare parts. The only thing mine needs is also the pressure gage. You can find almost anything for it on ebay. I found a new gage for $47.99, but I wasn't sure I wanted to pay that much. The item# is 120569366007 if your interested. I've also found a complete rebuild kit for the pneumatics, and the nylon protectors for over the tire iron to protect aluminum wheels. Mine is pretty original. If I can help you with any pictures or other info let me know.
When I was in the garage business long ago, I had the Hunter on car balancer. It will do a good job, but it is so hard to use. Especially since disc brakes. It's not good to have anything dragging when you are balancing. The bubble balancer always worked well for me even when I was in the bussiness. It's only the last couple years on newer, lighter front wheel drive daily drivers like my daughters Cavalier that the bubble isn't good enough.
I did buy the Greg Smith Equipment Atlas Combo with the TC229 tire changer and WB11 balancer and I like it very much. I'll never use it enough to pay for it but at least I know I can balance my wheels right. And it looks good in my shop. If I sell my old equipment, it won't be as big an investment.
Mike