You can get a set here: http://m.ebay.com/itm/Ground-Industries-Balistik-MAK-Tires-And-Silver-Terraintula-Hubs-qty-4-/201552445364?nav=SEARCH
I attached the sprocket using a 2mm thick g10 adapter. It works pretty well. There isn’t play in any direction, and it’s very easy to center the sprocket.
what is this/where can i get it?
Its just a custom cut g10 (garolite/fiberglass/pcb material) piece. Carbon fiber, aluminum, or even wood could work.
Sorry if this is obvious, but what do you mean g10? what is a g10?
oh my god im an idiot 
im assuming this is what you are talking about?
You’re assumption is correct 
That’s a great deal on those wheels!!
Yeah, I bought 2 sets. They are carbon fiber and aluminum construction. I was worried about the tires wearing too quickly, but they are holding up so far.
BTW: Epic build dude!!! That thing is mean looking!
how loud is that chain drive?
not too loud, it doesn’t strike me as extremely loud or annoying when I ride it, but it’s not as quiet as belt drive.