My guess is that he wants the length of Happ's long spacer, used on their comps/ultimates/etc...
The EXACT length is not super critical.
They just need to be long enough to hold tension on the spring and stick when fully assembled.
Happ's website looks like it lists them as .86"--if you go to the checkout cart and put in that part number.
They sell them for $0.71 ea.
I don't know if they have a minimum order though.
As far as substitutes go, anything that will fit around the shaft of the stick, not interfere with the throw on it, and not rub against other parts should work.
You might try getting some spacer material, designed to go around all-thread, and use a washer at the bottom of it.