Where do I find a Atari 2600?

I just found a the game "Raiders of the Lost Ark" for Atari 2600, and I was woundering where I can buy a system?

You can try E-Bay.

You can also download the 'Stella' emulator. It's a pretty cool Atari 2600 Emu. It has just about everything on it (including the only video game ever based on Raiders.) Do a Google search for Stella and you shouldn't have a problem.

Actually getting a physical 2600 might get a little pricey. The average pocketc calculator has more processing power these days, but those machines are sort of collector's items now.

It's not as hard as you'd think

Yes, you might have to dig some, but I'm sure you could find an Atari 2600 system on Ebay. I have also seen one for sale at my local video games store. It's really not too bad on price (I don't think it's more than $20 or so).
Other than that, you can check the flea market, His House, the Salvation Army, garage sales, yard sales, your grandparents' attic, etc.