I have lots of these stands and the bottom cymbal seat and sleeve were almost always missing when I acquired them. Here's what I did:
I simply cut about 1" off the top of the bottom tube, the side where the sleeve was that has the brass fitting on the inside. Make sure you cut it down far enough so don't run into that brass bushing!
I then just put this on the tube.
https://www.drumfactorydirect.com/index.php?main_page=product_info&products_id=9045
It's an exact fit around a 5/8" tube, which is what the 1123-1 uses. It's a little goofy looking, but fits perfectly, and it's less than $5. There are other aftermarket hi hat seats available, but NONE of them (except that Pearl shown above) fit around a 5/8" tube. To the best of my knowledge, the other Pearls, the Gibraltar and the "generic" ones that are available are all for 3/4" or 1/2" tubes. You can, if necessary, use the Gibraltar one shown here:
https://www.drumfactorydirect.com/index.php?main_page=product_info&products_id=6192
You just have to wrap the top of the tube with some duct tape or nylon tape to make the diameter bigger, because it's made for 3/4" tubes. I've used them before as well by measuring how far down on the tube the seat will go (mark it with a Sharpie), then cut the duct tape or nylon tape to that exact width, then just wrap the top of the tube with the tape and then pound the seat on with a rubber mallet. Still holding fine years later and it doesn't show at all , because the seat covers it.
I know lots of us folks want to keep things as original as possible, and I do as well most of the time. However, there are certain instances where the original was just a poor design or a pain in the rear, and to me, this is one of those instances.
Whatever route you choose...........Good Luck!