I bought that cable from Newark and it works, but it's too short plus it ships from the UK, so it's $15 shipping and took almost 2 weeks to get to me.
The cable you need to get access to the main 4 SATA ports on the motherboard after you install the Mac Pro RAID card is, in fact, quite standard, it's just that no one explained that and it took a lot of sleuthing to figure it out.
What you want to buy is a 0.5M (that is, half a meter long) SFF-8087 to 4x SATA internal cable. In typical FUD fashion, this is called several different things. The SFF-8087 connector is also called and "iPass", "Mini Multi-Lane", "Mini SAS 4i", and "Mini SATA 4i" connector. They're all the same thing. The SATA connector is whatever you want, but if you're going to use the SATACable's PCI bracket, you'll want SATA (or "SATA style" as they're called in the SAS spec) cable receptacle connectors, a.k.a. internal (a.k.a "L connector) SATA female connectors. You want straight as opposed to right-angle.
Oh, and to make it even more confusing, you can get these cables with or without "sidebands". You do not need or want sidebands, but if the cable that's easiest to buy has them, they won't hurt much. You can just not connect the sideband connector.
One other thing. Reminiscent of the RS232 days, these cables, even with this specific connector combination, come in two flavors. You want the one that connects the SFF-8087 to the Controller a.k.a. Host and the SATA connectors to the Backplane a.k.a. Target.
It's so obvious I can't believe I overlooked it. 🙂
Like I said, this is a standard cable you can buy from many vendors. But just to make it easy on you, here's one example of what you can buy. The Adaptec "ACK-I-mSASx4-4SATAx1 0.5m R", Adaptec Part Number 2247000-R, available from Mwave here:
http://www.mwave.com/mwave/skusearch.hmx?SCriteria=4240790
I also found one made by Micro Connectors on the shelf at Fry's.
One other note, if you're going to install the Mac Pro RAID card yourself, have this cable available to install at the same time. It's a major operation to get access to the connector on the motherboard that this cable connects to, but it's the same connector that you are unplugging to plug the built-in cable to the RAID card. Doing both at the same time will save you a lot of pain.