JPierre, I went several hundred hits into Google results, and couldn't find a single source for seeds or sets (cuttings) for Napier Grass/Elephant Grass. It must be available somewhere, because there appears to be widespread research on it at tropically located universities. Perhaps you could contact the Agriculture Department of such schools, and ask them.

It is apparently difficult to grow from seed, with low germination rates, and is most commonly grown from stem cuttings.

It dies back at temperatures below 10C, so you'll need a greenhouse (with a very high ceiling!), or it will only be an annual for you.