Agreeing with Burke, ChoralNet is a large site with lots of links to other good places. Argentinean and Latin American choral music is beautiful and not easy to find. If you are interested, possibly after some experience, I could send some traditional works for SATB that could be a pleasant surprise for your audience.

For new arrangements, I could also contact some excellent local musicians, but I guess that first of all your group would prefer something in the English/American/Australian tradition.

Un abrazo - Andrés in Buenos Aires