[ctuna]

I assume you can use Google.
Try Crutchfield for starter.
Or just do searches like " Speaker kits for BMW e90 "
or put the manufacturers name in that same search.
You will have to search hard for the best deals.
Or look in the audio build sticky for the master known speaker
list.
If you can afford a package and want some quality stuff
call Unexpected Creations in Edison, NJ

https://unexpectedcreations.com/mobile-audio/

As far as upgrades are concerned
Best System examples
Logic 7 upgrades
http://www.e90post.com/forums/showthread.php?t=826683
http://www.e90post.com/forums/showthread.php?t=590420
https://technicpnp.com/product/logic...-applications/
Base System Upgrades
http://www.e90post.com/forums/showthread.php?t=445266
http://www.1addicts.com/forums/showthread.php?t=634957
http://f30.bimmerpost.com/forums/sho....php?t=1003810
http://www.e90post.com/forums/showthread.php?t=822366
http://www.e90post.com/forums/showthread.php?t=581379
http://www.e90post.com/forums/showthread.php?t=451941
http://www.e90post.com/forums/showthread.php?t=540954
http://www.e90post.com/forums/showth...ghlight=Dotech
http://www.e90post.com/forums/showthread.php?t=495855
http://www.e90post.com/forums/showthread.php?t=494299
http://www.diymobileaudio.com/forum/...morel-jbl.html
http://www.e90post.com/forums/showth...ht=amp+upgrade
http://www.bimmerfest.com/forums/sho...d.php?t=550771
http://www.e90post.com/forums/showth...1#post16679904
http://www.e90post.com/forums/attach...1&d=1411521234
http://www.e90post.com/forums/showthread.php?t=1378833
base system wiring pre/post 3/09
http://www.e90post.com/forums/attach...1&d=1411521234
https://www.google.com/url?sa=t&rct=...tDpLJPcGkw_ui_
http://www.monsteraudiodesign.co.uk/
http://www.e90post.com/forums/showth...1#post16679904
HI Fi upgrades
http://www.e90post.com/forums/showth...ighlight=level
http://www.m3post.com/forums/showthread.php?t=540446
http://www.e90post.com/forums/showth...hlight=technic
http://www.e90post.com/forums/showthread.php?t=532585
http://www.e90post.com/forums/showthread.php?t=833581
http://www.m3post.com/forums/showthread.php?t=443043
http://www.e90post.com/forums/showthread.php?t=324214
https://www.bimmer-tech.net/blog/ite...-audio-for-bmw
http://www.e90post.com/forums/showth...hlight=level+3
http://www.e90post.com/forums/showth...ight=processor
http://www.e90post.com/forums/showth...1#post16679904
http://www.e90post.com/forums/showth...&highlight=BSW
http://www.bilstereoforum.se/showthread.php?t=2356
http://www.diymobileaudio.com/forum/...creations.html