I bought one of the Dakota Tactical MP5 pistols from Adam Webber of hkparts.net. Dakota Tactical MP5 pistols are built by Chopstix Kid. Both Adam and Chopstix Kid are sponsors of hkpro. Since the pistol is not on the California DOJ safe guns roster, I had to single shot exempt the pistol into California. Adam sent the lower receiver to me and the upper registered upper receiver to my 07 FFL. My FFL disabled the magazine release and installed a MP5 raddlock. The MP5 barrel is long enough (over six inches) so luckily, another barrel did not need to be installed.
Additionally, my buddy, ghilliebear2000 aka Jeff Walters, can build and send a MP5 clone right to your California FFL. The magazine release will have to be disabled and a raddlock installed. Jeff is registered with the California Firearms Licensee Check (CFLC) Program.