The limited editions for SR5 can still be bought online, but previous editions are long gone.
If somebody are still looking for these a few are on ebay right now:
SR3 Limited edition #675 Signed
SR3 Limited edition #723
SR4 Limited edition
SR4 20th Anniversary Limited edition
SR5 Limited edition, incl. free shipping
I've got nothing to do with any of those auctions, and only post them for others to be able to complete their collection.