The great descending then rising solo in the slow movement is the Wagner tuba. An inexpressibly magnificent passage.
And to the rest, Norman del Mar wrote in "Anatomy of the Orchestra" (highly recommended) that they generally 'hunt in quartets' so to speak - players rarely own them themselves, but an organisation (orchestra, opera company) will own a matched set of 2 tenors and 2 basses, which are played by the (often) 5-8th horn players.
I imagine you'd struggle to buy just a single instrument...
cheers,
Graeme
