big, major
chief, main, primary, principal
potential
private
official
state
the list of state sponsors of terrorism

commercial, corporate, industrial
title
the title sponsor of the rowing World Cup

look for, seek
attract, find, get
act as

back sb/sth, support sb/sth

money (esp. BrE)

sponsor for, sponsor of
I need to find some more sponsors for my charity bike ride.

a/the bill's sponsor (politics, esp. AmE)
Representative Ted Gatte, the bill's sponsor, hopes that the bill will be reintroduced on the House floor.

Sponsor is used with these nouns as the object:
award, bill, campaign, competition, concert, conference, contest, event, exhibition, expedition, festival, initiative, legislation, luncheon, meeting, programme, project, research, resolution, seminar, terror, terrorism, workshop