35mm lowering springs can be found from many places via Google. 50mm ones can be found via http://www.humphrisoxford.co.uk/rally/ these will cost around £100 more than the 35mm ones.
Splitters you can use are just from other cars, such as polo, Laguna, cupra. They mostly fit ok. Just need a bit of tinkering with. Lots have done banded wheels on here. Its just up to you.