I'm curious how you're eating through tires so quickly, do you drive quite a bit? I have 20 & 21" setups in OEM specs and the 21's don't seem to wear any faster than the 20's?
Anyhow, there's a lot of different spacer sizes for these vehicles. Many people here go through Ben at RG Sport, he's one of the vendors here (link below). If you can provide the offset of this 469 replica wheel, he can suggest a rear wheel spacer size. And I'd mention if you're looking to retain the OEM look, or more of a flush look, that will impact spacer size. Depending on offset there might not be a big enough spacer to go flush on a 10" rear wheel w/ the M Sport fender flares?
https://f15.bimmerpost.com/forums/member.php?u=76551