You must get it while creating bid invitation. double check since you are already attached to vendor organisation structure.Hope you have bidder user id and password. try to log in as bidder. if it so, you must be a bidder and Buyer should get a list of bidder.
i had same issue and bidder should have a role BUP001 role in BUT100 table.Hope that you have integrated the bidder w.r.t Vendor via Web portal.