Forgotten Ground Regained
Long Poems in Alliterative Verse
Whether the poem in question is a modernist eclogue, like Auden's Age of Anxietry, or a traditional epic, like Tolkien's The Fall of Arthur, alliterative verse works well as a vehicle for long form poetry.
For longer alliterative poems that have been published online or in larger collections,, check out the Epic Poems sampler.
Loosely Alliterative Long Poems Inspired by Alliterative Verse
The Stonecutter's Tale
Kellow-Bingham
(four-stress accentual with ryming couples, loosely alliterative)