Need some help finding a seat

I recently acquired my first motorcycle. a 1983 KZ550. It needed a wee bit of work but it is now running. Now my next obstacle is the seat. At the moment it does not have a seat and the back of the frame has been cut a little so I don't believe a factory seat will work. Since I am new to all this motorcycle stuff, I'm not sure where to start. Ideally I'd like a solo style seat but I'm not sure how to attach it. I'm already assuming I will have to take it to a machinist to get some kind of hinge or bracket welded on but I'm just not sure what exactly to get. Any help?

As the rear is no longer stock, there's no way to help without seeing some good pictures. Are the original mounting points still on the frame etc etc

eebbaayy photos are helpful for stuff like this. Just look at the various seats & seat hinges listed there for your bike. or similar models if you think something else will work.

here is what I'm working with.

The seat hinge mounts & hinge pins are still there, as is the seat latch.
You'll need the hinges & etc when you get a seat. Some eebbaayy sellers remove the hardware & sell it separately.

Like Martin said all your mounting hardware is still there. Take a stock seat and cut it down BUT one thing I would do is to take that part you cut off shorten it and lug weld it back on. I made a nice CSR Bobber doing that and cutting down the stock seat. Looked good and was comfortable while still having a lockable seat.

Ok I will take your advice and try to find a stock one and cut it down. Now what do you mean lug weld the part I cut off? are you talking about the frame? because I didn't cut that off, the owner before me did.

For strength & safety, you need to weld something in place of what was cut off.
Maybe ask the po if he still has the discarded section.

I did the same thing to a CSR and the back piece of the frame that he cut off had a step down in diameter. I trimmed that and then reinserted it into the frame tube and re-welded it. It surely stiffened up the back end so I could use the stock seat but cut down to a comfortable solo seat. It also provided a nice place to mount a rear light. See, this is how I cut my frame. Then I took the rear piece and inserted it and re-welded it back in. All I had to do then was cut down my seat and I have a comfortable locking seat. Finished it looked like this . or you could do something different. Just an example.

Nice job, Proxy. Was thinking about modding various frames in that fashion. Looks good. You don't happen to have any other photos of your bike that would show the side profile a little better, do you?

Another option would be to insert a fender. Measure the width between your frame over the back tire. You could probably find a used boat trailer fender for not a lot of money. Check local salvage yard. Scrap prices rule. If you can find something that fits, have it welded in. It will give you the support you need, protect your bike, and make it look cool.
You could also take advantage of how it is chopped off at the rear by mounting your lights like "end caps" inside the frame where it was cut. With a little thought, you could have your tail light and signals together in the same housing. Could be a cool, clean way to go.
Looks like you need a rear gas tank mount. Just a flat bar that mounts to frame and then fasten the tank with a bolt. Use a rubber grommet.
I'd get the tank mount set, cut off the stock hinges, and clean up the battery box, so you have a nice smooth, clean frame. Get a fender welded in for support (function and style). Take the rear shocks off and throw on some struts, lowering the back of the bike a couple inches. then put on a solo seat. You can make one. There is lots of info online. Pretty much make a pattern for your seat out of cardboard, transfer the shape of your pattern to some good thick sheet metal. Bend it to the desired shape. Get some hi density foam, leather, whatever, to make your padding and cover it. Put a hinge on the front and two springs on the back and you have a bobber.
Good luck

Before I added the MAC. She was comfortable and fun. Got a lot of attention too. Sold her a few weeks ago. Sold fast. Wish I had a dozen or so.