Give every student a cut-out hand and say that when they share, you will collect it until everyone has shared one time. Then, it's fair game for anyone to participate. The quiet students will be able to choose when they are going to raise their hand, while the highly expressive students simialrly decide when they will "cash-in" their time to talk.
Here's a free template (2 hands per page) to download: 2-hands.pdf
(I print mine on heavy cardstock paper, cut them in half and then laminate to last longer.)