Try something like this: http://www.newegg.com/Product/Product.aspx?Item=N82E16812189120&cm_re=pcie_adapter-_-12-189-120-_-Product
All you need to do is adapt the old 4-pin connectors to the 6-pin type used for PCI-E cards. Now if you don't have two free 4-pin connectors, that'll be a problem and you'll probably just want to get a new PSU. I wouldn't recommend getting a splitter, because then you'd be trying to pull about 25% more power over that particular rail than it's designed to take. At best you'd probably fry your PSU, but creating an electrical fire isn't out of the question.
Alright, just made some upgrades to my computer, among them a new video card (http://www.newegg.com/Product/Product.aspx?Item=N82E16814150438). I've come across a little trouble while trying to connect it to my power supply (http://www.thermaltakeusa.com/Product.aspx?C=1264&ID=1507). The problem is I don't have the 6 pin pci express power connectors that I need. The power supply is a couple of years old and I was using a different power connector for my old set up. I have no idea where the rest of the power connectors that came with the PSU are, seeing as I have moved a few times. I have searched on newegg and amazon as well as google looking to purchase the power connector I need but I can't seem t find a single seller. I even went to the manufactures's site and can't seem to find that specific cable I need. I have emailed the manufacturer about the possibility of obtaining some replacement cables but they have not gotten back to me yet.
Any ideas or suggestions of how I could get a hold of this piece or another available work around?