The bumpers and skirts turn up on eBay from time to time , as do the wheels .
The brabus stuff is far harder to find , I bought a brabus w168 with a dead engine from up north and a pal helped me bring it back and strip it.
Got the front and rear bumpers and wheels , had them painted , wheels refurbed , got the SWB AMG skirts from ebay as brabus didn't do skirts. Got a w168 brabus exhaust from a member on here. Spots for the brabus bumper were a pig to find as they are a funny size but got some from china in the end.
Gather the bits slowly and store them till ready.