The original governor spring part number for the 300B series was G47037, which appears to be obsolete. Unfortunately, I can't find a current number that it subs to.
The 300 round nose governor spring was VT4588 which subs to A30572. Similarly the 400B original part number was VT3066 which subs to A30127.
I didn't really answer your question, but maybe your parts man can hunt done the correct, current part number with these as background info.