You buy them direct from John Deere
They cost around 1 to 2 hours of techs charge out rate so will pay for itself the very first time you use it
And yes they are a step by step full repair manual aimed the owner, not a mechanic so everything is explained very clearly including what various bits do & how they do it, how to test each part and what the test results mean
Every JD owner should have them.
I was floundering when I first bough the service run, engines were fine but all the other bits were a mystery to me , then I had to buy a JD tech manual for a customers diesel mower .
That was a revelation and put an end to 2 years of struggling to repair mowers so I bought he LX & 100 series ones and became an expert overnight.
Even the engine sections were more detailed & better explained than the engine makers technical manual and in particular the B & S engines as they cover only a couple of variants so there is no confusion as there is wit the genuine B & S manual that tries to cover everything