the system 4 was repleced by the supper system 4 many years ago, and when I enquired at least ten years ago II was told that parts were no longer in stock for the older tanks.
you may find that the AP Classic tanks have many parts interchangeable. ALTHOUGH the cores seem to be of slightly different lengths. the AP tanks are sold as Arista as well as other brands.
https://www.freestylephoto.biz/5031-Arista-Classic-Double-Reel-Developing-Tank-with-Two-Reels.
my take is the Patterson reels are SLIGHTLY better than the Arista Classic reels, and the New artista reels are quite nice, but they have a loading ramp built in which is hard to use with 35mm
I also have some interchangeable parts that I have got with random darkroom equipment with the PHOTAX name as well as a similar tank that just says "made in Hong Kong"
the Newer Patterson tanks are in the very back of my emergency use only cupboard as I find the giant lids difficult to put on quickly and hard to be sure they are properly sealed. I would buy new old style tanks if they were still made.