Restricting availability of certain products to international customers??

I'm sure this has been asked a million times before, but if so, I haven't been able to find a thread about it specifically. Is it possible to make certain products unavailable to international customers? And if so, how would I go about doing that?

How will you know if your visitors are "local" or "international" before they register/login?

There are "IP sniffers" out there which will assist in rendering a site based on the visitors IP address, but there is no standard function within zencart.