Who else could have aided Gondor?

[lindil]

First off, Boromir, like Denethor viewed Gondor not only as the primary 'physical' resisitance to Sauron [though Rohan possibly had a more effective [if not larger fighting force], but also as the center of civilization. If one does not know about Lothlorien, this is probably rather uncontestable, but still myopic.

What help he may have hoped for is unclear, maybe on his trip to Rivendell, he began to get some inkiling of the remaining Northern Dunedain, and felt they should be more active instead of lurking in the wild. Aragorn it seems is essentially answering this implicit charge.

Also I think even though we do not hear towns spelled out, it is clear that there were far more Northmen/Woodmen/BEornings spread up and down the Vale of Anduin and in the East Bight of Mirkwood [that is a pretty massive chunk of missing forest anyhow!] and that though the level of organization was probably rather low, Gondor perhaps hoped something of a minor repeat of Riders from the North could happen again.

All rank speculation of course, we do not know how far Gondor had cast abroad for formal requests of help. Denethor seemed overly focused on what he could see with the Palantir, as opposed to what kind of alliances he could build with any Northern Woodmen.