Unfortunately, I can't think of a single Jamaican restaurant in the area. There are plenty if you head west to Inglewood, but that is at least 45 minutes' drive and probably more like an hour to an hour and a half.
There is or was a Jamaican restaurant in Corona, on McKinley just off Magnolia. I think it was called Tropical Grill. That's also very far out of the way.
Does it have to be Jamaican?
3848 N McKinley St Ste B, Corona, CA 92879
re: Das Ubergeek
If you're looking for ethnic (as in not American) food, you'll be within easy striking distance of a lot of Mexican, a great deal of Vietnamese, Chinese, Korean, Salvadorean, Thai... I suggest searching "Anaheim Convention Center" and "Disneyland" since there have been lots of threads lately.