In the official BMW acessories line for the X1 you indeed have 19" rims available - though nothing that particularly attracts me.
They have these 19" chrome rims:
8J x 19 225/40 R19W forward,
9J x 19 255/35 R19W back
but the set (rims+tires) costs nearly 4.500€ here in Portugal.
(the non-chromed set costs 3.500€)
Even though I love the 19" (and non-official 20" rims) for its looks, the truth is the 18" wheels are the best option for the X1, particularly if you live a country like Portugal where even the "good roads" are not particularly good.