I don't think the factory gives out spring rates. Just spring sag or collapse. Book gives you a length range to be within spec or replace. However, I would imagine a spring company would have to know the spring numbers, so they can sell you a stiffer/softer spring from that setting.
And just a note in this area... Today's springs come in half and whole increments. That means, (where is me math man?), this more becomes an art. You more or less do not throw in a set of springs and be off riding. You can literally dial in more combos of front end spring rates.
That math says, you buy an 8.5 spring pound rate for one fork setting, stick a 9 pound in the other leg, you come up with an 8.75 combination. If you shelled out for 5 sets of springs @ 8/9/10/8.5/9.5, see where [the art of the suspension] tuning becomes more difficult to achieve? You could add one of the stock springs where you have 6 sets total. And that's just for the front end.
See where a straight set might be too harsh/soft, but a step down/up in the math combo, you can keep records of what worked and what didn't? With all the rebound and compression settings, cheeze us wad a mess to get it dialed in!
Known to be at tech thread abuser. I like lying to animals too.