I do not know of a place. You might need to fabricate a spring mount, which can be nothing more than a small strip of metal (
in GREEN) drilled on both ends. One hole drilled to hook the spring to and another hole drilled to fasten the strip to the existing tab on the engine (that is already pre-drilled).
View attachment 151949
I drew the head of a philips screw to indicate where it could be fastened to the engine. Heck, you could even put an L bend on the right end so it sort of clips around that tab there and keeps it all aligned.
Otherwise I am trying to find out how the factory hooked up the throttle on these engines. There's a lot of go karts and minibikes that had this type of Tecumseh OHV engine but they sort of pre-date the internet era that we are now in.