From your model and type numbers it appears that the correct part number for the governor spring is 260902, and the top no load setting should be 3000 rpm.
The 260902 is shown as still available with a retail price of £8.16 inc vat.
Section 5 of the manual, page 25 of the section shows using a simple home made tool to “ tweak” the spring anchor. A piece of 8mm rod with a slot cut into one end and an L bend to aid controlled tweaking.8
