I'm about to offer a tiny sliver of information, but it may be helpful. There
is definately a company that makes time capsules, I've seen their brochures.
Now, who they are and where they are is another thing, but maybe just knowing
they exist, you can locate them on the Net. I recall that the capsules look
like giant bullets, come in various sizes, and are made of different
materials, depending on your intentions. I hope this crumb helps.

Ceres Bainbridge