Liturgical feast days? Where in Scripture?
Nowhere in Scripture does Scripture claim that Scripture has every jot and tittle of Christian practice spelled out in detail.
You don't even know what books constitute Scripture apart from the authority of the Church. Go ahead: prove from Scripture that Romans or Galatians is Scripture. You can't do it. Even John Calvin admitted that it can't be done. R.C. Sproul admits that it can't be done. Apply your standard rigorously, and you'd have to throw the NT away.