Upgrade M17x R2 to Crossfire

It's been a while since I posted here... But I revived my old M17x R2 and I want to upgrade it to Crossfire.

Currently running single ATI Mobility Radeon HD 5870, but I have no idea where or how to buy another one and the Crossfire Cable (?)

Anyone can help me? And now that we're at the subject, any info to upgrade the Processor? I have i5-520M and want an i7.