Looking for a place to buy a spring stacking kit, Deycore used to sell one but it isn't listed and they say they don't sell springs anymore.
Does anyone have another place to purchase ?

it basically is an aluminum shim with crossover rings.

Never mind

Deycore still sells the spring separators and crossover rings , just no springs.

What is a spring stacking kit? What does it do?

basically it's a spacer and some rings.
What it does is allow you to run two springs with different rates. The rings are what crosses over one spring to another. It is WAY more technical than that but you can run a soft spring for the smaller bumps and when the stuff gets big they crossover into a heavier spring. Asking one spring to be usable in multiple situations is a tough. These are used on the front shock springs and sometimes on the front track spring. Dirtbike guys have been doing it for a long time.

So it's kind of like multi-rate springs except it's in 2 springs instead of one spring? Sounds like it would work good.

Depending on the design they can be murder on your threaded shock bodies though. I think that is why polaris only used them for one or two years from the factory. My 02 shock bodies had hardly any teeth on the threads from using them.