A Brave from Hong Kong did the unimaginable - flash X300 BIOS on A300 board. It's possible, but according to his statements, most BIOS functions and options are dummy. And the system as a whole is unstable.
I do have AFUWIN windows flash application. But now I'm using A300 as my work machine and I don't have other spare PC around, so I can't take the risk of brick my work machine.
If there are any brave (and reckless maybe?) souls, here is the AFUWIN application with X300 BIOS file. Caution! I...
Unfortunately, they don't ship overseas. Perhaps try other retailers in Taiwan or Europe? Also just as michang64 mentioned, in Taiwan at retail you have to build a whole new PC as prerequisite to buy a Renoir as CPU of choice. It's not sold separately.