One of the key points in the definition of a so-called assault weapon is its capability to accept detachable mags.
Now, if the same semi-auto firearm had a fixed mag, it would not be an "assault weapon", and could accept and have any and all of the "eeevil features" mentioned in the ban.
For example, DSA makes an FAL with either a 10 or 20 rd fixed mag, loading via stripper clips through the top of the receiver. It's available in CA as a new purchase, whereas the regular, detachable mag FAL isn't.
An M1 Garand uses 8-rd clips, so it can have a bayonet and a flash-suppressor.
I'm not a lawyer, so check out the above. In addition, local and/or state laws may have an impact as well. Good luck!