I presume you are referring to the FNX-45. It's not on the CA DOJ roster, so you may have to purchase from an out of state retailer and go through the SSE transfer process. I just picked up my FDE last night from OC Armory (which does SSEs). Note that some CA retailers have off roster pistols available for purchase via SSE - last I checked, EBR Works (in Newbury Park) has the FDE in stock and available for SSE. I purchased a FNS-9 from them a few months ago.
Second EBR works, recently got my FNS-9 from them too. Also check out Ed's Tactical Eds Tactical Armory Online Store They don't have it listed but I talked to the guys there recently and they are working on getting an FNX-45 (SSE) for sale soon.