I, too, fell in love with mangosteens while in Singapore last year. I've tried buying them from some of the Asian grocery stores in Falls Church, VA (where they're available frozen), but they've been absolutely awful. I imagine the cold kills any hitchhiking bugs... but it also radically alters the taste and texture of this wonderful fruit.

I recommend seeking out mangosteen juice as an alternative. I saw several companies with mangosteen products at 2006 food-industry trade shows so keep your eyes open as you swing through your favorite grocery store.