Hi. I was a member of NU's Hawaii Club as an undergrad and still help them with their annual luau. As Pucca suggests, the club itself prepares the food served at its event. The decorations (fresh flowers/foliage and the like) are typically donated by friends and family and shipped from Hawaii shortly before the event. This is the SOP for the University Hawaii Club luau across the nation.
In any case, I'll post some notes about smaller luau-type events I've hosted on my own, in case you might be interested...
The basic luau fare is not at all complicated. Check out
http://onokinegrindz.typepad.com/ono_kine_grindz/home_cooking/ or the luau section of
http://alohaworld.com to see for yourself. Ti leaves can generally be omitted or replaced by banana leaves, and taro leaves can often be found in Asian or Caribbean groceries. I've done the cooking for my events; but with the number of guests you're talking about, it's clearly not an option for you. Given the simplicity of the dishes and availability of their ingredients (you honestly can't screw this stuff up), you should be able to convince an open-minded caterer to handle the food for you.
IMO, the Tiki theme is the epitome of gaudy. A ballroom, or a large, private backyard would make better venues than a Tiki-themed bar or restaurant (no offense, MJ, as I do think that your suggestion would be absolutely perfect for a fun, casual party). Adding tropical foliage and subtle accents onto white tablecloths is more than enough to convey the theme without conjuring images of bad cocktails and tacky aloha shirts.
As far as tropical flora, I can suggest a few to you. Pikake is a type of Jasmine Sambac, which isn't sold here very often but can be conveniently ordered from growers in the southern states. It's strung into lei resembling strands of pearls, and I believe it's also the same flower used in China to create jasmine tea. The fragrance of fresh pikake, if you've never experiened it, is incredible. Tiare--a Tahitian gardenia with a very nice fragrance--is often available potted from local garden stores (I've even seen it at Sam's Club). Like most gardenias, it's pretty fickle; so if you want to put the blossoms into service, buy right before your event--presumably shortly after the grower has forced a bloom. Purple and white dendrobiums are very common in Hawaii--they are often made into durable, though scentless, flower lei. Against a background of dark foliage like ti leaves, scattered dendrobiums can provide a subtle tropical look. Hawaiian ti leaves are a type of cordyline (sp?). The red version usually shows up at Home Depot's garden centers sometime around the end of spring. You could try calling some florists in Hawaii and asking them to ship green ones to you. The leaves are very durable and should make the trip just fine. Dendrobiums are shippable, too.
The combination of fresh-cut pineapple, fresh coconut, and some blooming fragrant plants (eg pikake, tiare, white ginger, tuberose) is my standard recipe for oflactory ambience. The resulting fragrance screams tropical and is probably the one thing that guests have enjoyed the most. For the more formal gatherings, some tropical-inspired arrangements from a local florist complete the look.