You can save yourself some trouble by buying the cable ready made up, they are available via eBay. I would recommend www.uricables.com for a fast and efficient service. You can order from them directly or via their eBay listing.

That said this is not a complicated cable, and it would be reasonably easy for you to put one together yourself after you have studied the photos below.

It is not clear in the photo but you should insert a 20K resistor into the green wire Rx wire. This may have already been done if you buy a made-up cable from the internet. Ignore the other resistor in the photo, this was a failure!