UPDATE:
So I'm aparently an idiot, while my LBS of choice is small (Larry's bikes plus on 87th and 2nd) they do have everything! The bags were tucked into a cage in the corner but they had several different ones, including the TOPEAK explorer MTX DXP trunk bag with the panniers. Picked it up today and so far so good. Looks to be a good size for my needs. Going to test it out right now!