Yes, I have a few small ones. There's not many of us still have things with square head fasteners!
I find the occasional square nut on the old machines I have worked on.
Engels Coach Shop, on You Tube deal with these old square nuts in every video. I should not be surprised, but , these square nuts are still available.
I made a few from square bar stock. Almost a century ago, 12 pitch on 1/2" bolts was dropped for the new standard of 13tpi for the course threads.
One of the bent shafts for my WF and John Barnes camelback drill press needed to be replaced. The shaft was a non-standard size today, so I bought the next size up and turned it down. I had to make the replacement for the missing nut. I had to single point turn the threads. Luckily, my Myford Super 7 had gearing for 12 pitch. I made a souvenir nut when I turned a left hand thread/12tpi. This was good practice for getting the final thread right. (pun intended)
I shop built the (red) gear guard and the red crank for the ACME table lift. I sacrificed a socket to make the crank. A rare earth magnet, epoxied in the socket, holds the crank on. It takes a significant tug to pull the crank off. (you know what I mean

)
I had planned to use an 80 year old GE electric motor to power the drillpress. My son took it apart so the motor could be super cleaned. After about 30 minutes in the ultrasonic bath, I put the armature in my lathe, on the highest RPM for 30 minutes. Lots of water and dirt came out. I put the armature out in the hot sun for a day. The motor was given new paint, lubricated and reassembled. Time for a test run. In less than a second the motor exploded and there were copper bits rolling around the shop and the loud humming stopped. A rebuild was quoted at $1K. I bought a new 1HP US MOTOR replacement.
I want to sell this 1100 pound WF and John Barnes drillpress. I have 2 grand into it, but, we can talk about this.