[JThiessen]

Most definitley use a collet. Chucks are only good for vertical forces, collets are made to also hold horizontal forces.

Your table should have long slots in it. A bolt head will fit into the slot (such that the bolt is upside down). You can do several things with these - drill a couple holes in the work piece, and bolt the workpiece down, or you can purchase clamping systems for it. Your owners manual should have some tips on this.

As fas as where to obtain aluminum - locally in the northwest we get it from Grainger, Ryerson, and other local metal suppliers. Maybe call some of your local welding shops and see where they get theirs, and they may have scrap they will sell you.