Default [Q] Get proprietary blobs to build curstom ROM


I want to create an AOSP ROM (KK 4.4) for my Samsung Galaxy S4 Mini but for this I have to get the specific proprietary blobs. Now my question is where can I get them for Android KitKat? Do I have to build my own, port them from another phone or can I extract them from the stock Rom which is Android 4.2? I do not have much experience in building ROMs from source but I read a lot about this in tutorials and I think it would be possible for me to build an AOSP Rom if I have this proprietary blobs.

CyanogenMod (11 is avialbe for my smartphone) is created from AOSP so it must be poosible to create a "normal" AOSP Rom but from where get the CyanogenMod developers the proprietary blobs? Each phone has other proprietary blobs but for each phone it is possible to create unofficial ROMs with higher Android versions. How is that possible although the drivers and so on are not open source (except the Nexus Devices)? From where can I get the proprietary blobs?