HD 3650 power supply

I have an HP Pavilion a810n and I bought a Radeon HD 3650 graphics card to improve the graphics capability in a 3D Architecture program I use. When I tried to install the card I needed to connect a power cable to the card. The card has a 4 large pin connection. The Pavilion has some spare smaller power connectors that reach the card but, the only large pin connection it had for a spare did not reach the card. Where can I find a extention cable for the large pin supply or adapter for the smaller power supply connections?