They are sized - too big and far too big if I remember correctly. Actually, I think only a couple of size 'bands' that are height dependent. Mine says 117cm, which I can confirm drowns someone who is 163cm tall.
And no, your MCR doesn't bulk buy, but it does buy off any leavers who wish to sell, so will probably have a few available as term starts. Email the current MCR President who will confirm they are still going to run the scheme this year.