Personally I just stalk thrift stores like mad. (I got a really great jacket for my Ouran cosplay by doing that. It's a teeny bit too big for me but it helps hide the days when I don't feel like wearing my binder with it) But for your group it would be harder to match the shades unless you got really lucky.
You could sew it...? You could get a pattern on sale for 1.99 at Joanns/Hobby Lobby and probably drop around $25 in fabric per blazer depending on the quality of fabric and whether or not you get 40% off coupons for the fabric. But they would all match and be sized perfectly.
My cosplay reference guide site: www.cosbreaks.com
Past & current cosplays: Death (Sandman), fem!Sam Winchester (Supernatural), Eleventh Doctor (Doctor Who), genderbent!Haruhi (TMOHS), Tamaki (Ouran), Castiel (Supernatural), L (Deathnote)
Cosplay dreams: Takuto (Fullmoon wo Sagashite), Break (Pandora Hearts), Watanuki Kimihiro (xxxHolic), Ciel Phantomhive (Black Butler), nearly everyone from Pandora Hearts and Tsubasa