GasGas EC 300 2011 need new shock spring

[drorsdd]

Hi All
I am very happy i found this forum, been reading most of the suspension posts but still have some questions.

I have a new GasGas EC 300 Racing 2011, i am from Israel so the racing model here comes with the Marzocchi 48 mm front and Ohlins 888 rear.

my weight is 200 pound witout gear (so i assume 10-20 pounds more with gear)
rear shock stock spring is 5.2, and here is the problem:
with shock spring preload at 10mm from full open i get a static sag of 35mm and rider sag 135mm, so i had to close shock preload to 25mm from full open and now i get the desired 105mm rider sag but the static sag is only 20mm.

all this tells me my rear shock spring rate is too soft, any idea what spring rate i need and where can i get it in the USA or Europe?

Thanks for the help. (can add pictures if its any help)