If you're planning a clarinet choir concert, why not have a "Four Seasons" theme? Here is some clarinet choir music for each season, available on Sheet Music Plus.
Spring: "Now is the Month of Maying" by Thomas Morley. Score here. Parts here.
Or Grieg's "Last Spring," the second of his Two Elegiac Melodies. Score here. Parts here.
Summer: "Sommarsang" ("Summer Song") by Wilhelm Olof Peterson-Berger. Score here. Parts here.
Fall: "Automne" ("Autumn") by Cecile Chaminade. Score here. Parts here.
Winter: "February Sunlight" by Emily Gray. Score here. Parts here.
(or choose a Christmas carol arrangement - details in this blog entry.)
For a clarinet choir piece including all seasons, you might be interested in "Seasonal Sketches" by Everett Gates, available on JW Pepper.