I'm looking for an alternative to Hahnemuhle Fine Art Pearl (320gsm weight) paper that is available in sheets 17" x 25".
Apart from several Red River papers, and the Harman Gloss that Howard pointed out, you are out of luck.
Moab does have some papers, including Somerset Photo Satin, in A2, which is approximately 16.5" × 23.4". Museo has Silver Rag in US Arch D (24" x 36"), which cuts down nicely into two 17" x 24" sheets, with only two inches of waste (and no decurling).
Otherwise, there is no alternative, that I know of, to cutting from rolls.