Don't send them to CA, if there not legal in CA. No brainer. Very politely, tell the buyer this.
Wait, the round limitation was overruled by (OMG) the 9th Circuit Court. The CA limit on magazine capacity is now dead. 30 round mags are now legal in CA.
If I may humbly suggest - while stating you will ship to states were legal - and not ship to states were banned or prohibited...
Include a brief I will not ship to disputed zones inside Canada or the conus while unsettled or under appeal for my own safety and to maintain compliance with batfe rules and individual state laws.
Your hole card and your "out".
You have the right attitude and have rigidly maintained your stance - take a a knee and a breath and stop panicking or losing sleep.
You done good and done right and we applaud you.
Getting customer support and a refund of fees may take 6 months - may take more or less depending on covid QED the election outcome.
Seek inner peace and repost and resell and regain some funds.
Do not keep complaining to GB as it puts you at the back of the line as a new request.
We got your back.
You are okay.