Game looks interesting to me and I'm thinking about picking up the core set. Will I ever need/want to buy the same core or expansion set more than once? For example in X-Wing/Armada you often want multiple core/expansion sets of the same thing to give yourself more options when building your fleet.

Nope, there is one scenario to download from ffg that require two sets but otherwise no. The scenario is just a huge battle variant.

Thanks!

Is this game even available any more? The core set says "Not Available" as opposed to "Out of Stock".

This looks like one of the more interesting GoT games, but I took that to mean they're not making it anymore.