computer,
I'm not convinced you can just illuminate an area with IR for a standard webcam! The reason you see a white light, is because of the nature of CCD. (charged-couple device) This is the part of the camera that actually 'sees'. You get the same effect with camcorders, digital cameras and some camera phones.
I think in order to actually illuminate a worthwhile area with IR, you would need so many, and they would have to be very powerful. Also you wont get that cool military style special forces green look either!
I'd say it is impractical to do it! Depending on your application your better off using a special night time cctv camera, or just turning the lights on!
But if you'd want to have a go, just search for IR LED on any of the sites you mentioned, order the biggest sort with the highest candella rating (mcd) you can find. Order as many as you can bear, and attempt to make a nice circular array with them. If you position this under your webcam, facing the same way, that will achieve the best effect possible. But I do think that you will be dissapointed with the result!