Just finishing building my first AR (5.45x39 FrankenAR) Love the way they just screw and snap together. Thinking about doing one in 6.5 Grendel. Is the round easy to get locally?

nope

6.5 Grendel is just one of those rounds that look so good on paper, has a small but cult following, and actually seems to perform as advertised.  Unfortunately, it just seems so impossible to get the ammo, especially out here.

That being said, I've read about guys getting their AK's rechambered in 6.5 and that just sounds fantastic.

Damn near impossible to find loaded ammo in Hawaii!!!

Some guys shoot it locally but either you buy a case at $25-$30 (I forget, but pretty damned expensive)  per 20rd box when they come in stock once a year, if you are lucky enough to be there when it comes in.   OR you have to reload.  Lots of reloading material available online from Midway or Alexander Arms. 

The only loaded ammo option I have seen here is the Hornady match ammo which use the Amax 123gr which does explain the cost.  I have heard that Wolf makes some cheaper option but never seen it in Hawaii. 

I would consider a .300 blackout or 6.8 SPC if you are looking for something unusual but available.  I have owned neiher but seem right on the line of exotic vs availability.

I also heard of people here fire forming AK brass.  I don't know the process but that is another possibility.