FUD, and half the facts
You can legally have an HK45 in Kali.
1. Private party sale within the state
2. LEO exemption
3. Single shot exemption with out of state FFL
4. Send to a Cali FFL who does the single shot in house, no third party needed, one stop shop
Cliffs notes version:
-Ask the purchaser if he knows what he is doing with buying an "off-roster" pistol.
-If the answer is yes, ship it to the FFL he wants it to go to, whether it is in state, or an out of state middle man FFL. If the guy doesn't know what he is doing, it is still perfectly legal for you to ship ANY HANDGUN into California. The receiving FFL just can't transfer. No skin off you, the buyer screwed himself. Just make sure you get paid first.
-You can legally ship ANY handgun to California, HK45 included. The FFL can not transfer it to the buyer unless it is on the safe handgun list, or unless it falls under the single shot exemption. Some FFLs in California do the "SSE" in house when it arrives, and transfer to the purchaser as a single shot pistol, no middle man needed.
-Option B: Ship it to a third party FFL, like Table Rock Arms mentioned above, who will SSE the gun and send it in.
-It is ONLY illegal for the FFL to transfer to the purchaser a non-exempt gun. It is NOT illegal for you to send the gun in.
-It is all up to the purchaser to sort out how he wants to get the gun in. From the out-of-state sellers stand point, it doesn't matter. Get your money, ship to the FFL, if the receiving FFL can't transfer it to the purchaser, the buyer is stuck with a gun he can't get out of the FFL.