You know, I went back and found when I originally started making up hex bar kits and was shocked - Shocked, I say! - to find that it started back in 2006 with @DannyP and @RS-60 mark getting hit in the head by Heim bearing Cosmic Rays at the same time, even though they live 3,000 miles apart! They came up with very similar designs for their respective Spyders (which we all know are a little weird to start with) and I figured, "Wha' the hey?" and tried it on my Speedster and then modified it a little bit to put my own spin on it (and use locally available parts) and that's what's been going out in the kits.
I also found that, even back then, there were a couple of DIY kits on The Samba that were selling for over $100 bucks ( Seriously? ) so I thought that my kit of quality parts either sourced from industrial suppliers or Aircraft Spruce at $50 bucks was a steal.
Regarding the centering springs, I went with slightly heavier ones because I noticed that when the gas pedal is pressed, the entire hex bar shifts to one side. Quite a bit. That's why the spacers are in there - To limit the sideways shift and they should, ideally, have a gap between the spacer and Heim bearing thrust surface (or thrust washer, if you use one between them) of 1/8" - 3/16" per side when the engine is cold. That gap will grow a few thousandths when the engine warms up and everything will be happy. So you can see, with all of the different sizes of engines out there, that those spacers might want to be a slightly different length than the 3/4" versions in my kit (although that length seems to be fine for all of the kits I've shipped) and I tell you how to adjust that.
Anyway, now you have the info to DIY a hex bar upgrade. Good Luck!