The discription at buykawasaki states the spring rate. There are usually the optional springs listed as well with a slight difference in part #'s and the spec code says (option).
SPRING,SHOCKABSORBER,K=5.0,BLU
SPRING,SHOCKABSORBER,K=4.8,BLU (OPTION)
SPRING,SHOCKABSORBER,K=5.2,BLU (OPTION)
This example is cut and pasted from their site for a 1999 KDX220R and demonstrates that the stock spring is 5.0 with optional 4.8 and 5.2Kg rate springs.
The 1993 KDX spring is 4.6 with 4.4 and 4.8 as options. 5.0 will probably be too much for general woods and play riding as it is beyond the rates of their optional springs. I'm guessing that the reason for a difference in stock spring rates for the 2 different years is due to suspension geometry.
Now, go out there and figure out your suspension and be sure to update us with your results.