There are BMW space savers available, but they will probably only fit on the rear due to the 380mm front brakes.
https://www.ebay.co.uk/itm/322476590683
Watch out for kits for the newer models, FWD 2er, G11, G12, G30, i3, i8, etc I understand these cars have adopted a new PCD (bolt pattern).
19" space savers are available for X5/X6, but I think due to the tyre size they may foul the arches on a 1-4 series car.