Christ is the "substance" in that He is the fulfillment of the whole law. He IS (present tense) the fulfillment of the whole law, including the feasts:
"Christ is the END of the law for righteousness to everyone who believes" (Rom. 10:4).
Now you want Christ + the feasts + the letter + the sabbath and + everything else. But the Protestant Reformation had it right. It is NOT Christ + anything. IT IS "SOLA CHRISTOS", THAT IS CHRIST ALONE!!!!!!!!!!!!