Greetings,

I hope I understood your question properly. In Rashi it seems that the Melachos are learned from the construction of the Mishkan, and not from the work done in it after it was erected. Therefore, he resorted to sowing and harvesting for dyeing the Yeri'os, and not the harvesting of the wheat for the Menachos. From Rav Hai Gaon's response (Otzar ha'Geonim, Shabbos 49a, Siman 157; see link below) it is clear that he learned the Melachos also from the work done for the Korbanos and Menachos, and not only in the preparation of the Mishkan.

This topic is discussed at length in several sources. One of the best sources I can offer is the introduction to Sefer Eglei Tal.

I hope this was helpful. Let me know if you have additional questions.

Aharon Steiner

Link to Otzar ha'Geonim:

https://hebrewbooks.org/pdfpager.aspx?req=38273&st=&pgnum=59