Colour Team Groups - F.A. Cup Finalists 1976
Martin Bennett has provided a photo of this large poster. As it states Finalists, not Winners it's possible there's also a Manchester United poster too. Southampton won the Final 1-0.
UPDATE (02-08-2019 12:11): Manchester United added.
Southampton - F.A. Cup Finalists 1976
Manchester United - F.A. Cup Finalists 1976