Who else could have aided Gondor?

[Inziladun]

Originally Posted by Rhod the Red

The dwarves of the Blue Mountains.

But that'd mean them giving up mining there, the Elves of the Grey Havens lending/staffing the craft there to take them to Gondor.

That leads to a question of who would have aided Gondor. I would think any available Dwarves would have seen Erebor as a more important focus for any military action, and would have gone to Dain first.