PLease advise solution

Ok i built my comp a while back now and was thinking of upgrading my graphics card. Now i have at the moment an asus pk5 premium black pearl edition with a power colour gpu which has since been discontinued!!

instead of upgrading to a different card i always wanted to get another 3850 working in crossfire as i think this would be best value for money.

Thing is they dont make the card anymore and i cant find one for love nor money!!

here is the exact spec

AX4850 1GBD3-PPH
Graphics Engine RADEON HD4850
Video Memory 1GB GDDR3
Engine Clock 665MHz
Memory Clock 950Mhz x 2
Memory Interface 256bit
DirectX Support 10.1
Bus Standard PCIE 2.0
Video Input
VGA Output Yes, By DVI to VGA converter
HDTV Output Yes, By HDTV Cable
TV Output Yes
DVI Output Dual DVI
Dual-link DVI Yes
HDMI Support Yes, By DVI to HDMI Adapter
HDCP Support Yes

Now there is a simmilar 1 to this made by power colour but the clock speed is lower and the heat sink is different. My one has a cool copper heat sink.

Ok so you can see my dilema, i've heard you can crossfire same card of different brands but i dont know which one to get. I'm no genuis at this rig building stuff.

So do i bite the bullet sell my 3850 which is probably worth sod all as i dont have box anymore, and by 2 4870's and put em in crossfire. That would cost me about £200

Or do i get a similar 3850 and hope to god that it works in crossfire mode with my existing.

Obviosly the latter option is more desirable as it would cost half as much.

PLEASE HELP!!