From Volume One (an inexpensive book, by the way):There's a pair of compilations of excerpts called "The Orchestral Saxophonist," vols 1 and 2, available from various sheet music retailers and probably Amazon and Ebay. Some of the excerpts seem like little snippets and may not be long enough to meet your requirements, but it's a starting place.
One can certainly compile a very substantial solo part by piecing together some excerpts from the First and Second L'arlesienne Suites by Bizet.
The alto solo in "Pictures at an Exhibition" is not lengthy, but it's so important in the repertoire that it might be accepted all by itself. Tone is exceedingly important here.
Check out the material by Walton and Vaughan Williams -- there are some tricky passages. This could make a good choice for a more technical excerpt.
"Symphonic Dances" by Rachmaninoff also could be a good choice.