There are a lot of off-white plastics, but the one that probably looks the most like ivory is Elforyn (There are 2 varieties of Elforyn: one is snow white, one is off-white with streaks of tan in it to look like the grain in ivory.).
I don't know you, and I'm not accusing you of it, but the way you worded it ("Something that unless you knew people would think its ivory.") kind of sounds a little... well... fraudulent.
If you want it to look like ivory, get ivory. Why do you want it to look like ivory but not actually be ivory? If it's a moral issue, then why mimic that which you find immoral? If it's a price issue, just bite the bullet and get the real thing.
As far as a resource for highly figured wood, as per the rules, we're not supposed to give out suppliers names. In addition to the Forum rules, when cue makers find a really good wood supplier, they tend to keep that info to themselves. Fortunately, searching Google for an hour or so should give you a lot of supplier names.