The innovativerc cups are made of 6082-t6 aluminium which is supposed to be stronger than 7075. They're more expensive the the Losi HD cups, but InnovativeRc offers free shipping on orders over £25.

edit: they come with these parts:
3x Diff Cup case in Clear/Silver anodize.
3x Diff Gasket.
6x 2.5x12mm hardened Gear Pins.
12x M3x12mm Countersunk socket cap Screws.
6x Diff cup O-rings.