Asclepias tuberosa does not need any cold stratification. They are immediate germinators. That is one of the problems folks encounter as they sow them in the fall when they collect them and usually within 2-3 weeks they sprout and then along comes cold weather and kills them before they have a chance to harden off. To have plants ready for you MArch plant sale you will need to start them in a greenhouse or indooors. The greenhouse will do much better as you usually can't supply enough sun for them to grow properly. Good Luck.
Mark (wildflowerman_2000)