One way to check your actuator:
Do this cold, unless you have restaurant fingers
Remove the vac hose to the actuator
Remove the wastegate clip and unfasten the end
"Gently" (it may take some force) push the rod into the actuator housing.
Place your finger over the vac nipple
release the rod pressure
remove your finger,
if the can held vac you'll hear a small sucking noise.--Good
No vac - Bad
This doesn't check the spring, but ensures that your diaphram is intact, takes thirty seconds to perform and is free...
You should be able to use any actuator that can be adjusted to you desired boost. One off a T3 would work, but you might have to fab up a bracket?
IIRC I saw a pic one (Honda?) using a dog chain, and a spring, mounted it to the actuator on the engine block, damnest ingenuity ever...