You can try and check out Audison, Bavsound and Alpha One as I've seen some of them being fitted online. Though for my five door I might try and use speakers from focal, as my shop told me they fit. Goodluck OP!!

 

We ordered a Cooper 5 door in Dec. without the HK as it was not available as well. Planning the following upgrade:

Amp: Audiotec Fisher MATCH M5.4 DSP
Front door: Audison APBMW X4E
Underseat: MATCH MW8BMW
Audiotec Wifi Control

Speakers are OEM replacement including connectors. Amp is plug and play through an additional connector. WIFI Control will allow setting adjustments with a phone and dsp setup with laptop. Not cheap though.

 

These are basic stage 1 Audison kits I prepared ready to be installed once my F55 Exclusive expect to be delivered in March. It’s not cheap! but you would get an excellence sound quality.

I left rear speakers alone as no one sit at the back. I have to purchase HK A-Pillars for installing a pair of tweeters.

Also, DYNAMAT Xtreme Sound deadening for both front door panels, under subs and boot.

 

Look forward to hearing how trhis goes. The base systems in the BMW/MINI's are horrible in my opinion. We have the HK in our 2016.