OK, that explains it. Sun Tour (the real Sun Tour, not the current owners of the name) has been out of business since the mid-1990's and I don't think they ever sold freewheel repair parts as separate items, and certainly not to the end-user. So, the only source for parts is to cannibalize another freewheel.

I recall the days when every bike shop had a Sun Tour "Cog Board" with every individual cog they made and you could, within reason, build any configuration freewheel you wished. Indexing and the advent of more and more "speeds" ended that.