I have a PSP 2006 (Got it from Hong Kong), right now running 5.00M33-6 and will be changing to 5.50GEN-D3 soon.
I ordered it from console-tuning.com, they also sale it from other places too. If you lived near me and I know you, I probably will ask you to do it for me.
I always had bad luck doing things to PSPs, but somehow, it only affects mine. I always fix other people's psp perfectly, and have no one to fix mine.