Just go to your local hardware store...
They usually have all kinds of chain there.
Unless of course you want it complete wirth ball bearings or swivels.
You can buy just the chain connection with ball bearings in many
online shops (just look through the partners on the bottom of the page).
If you prefer swivels there are some pretty good tutorials in this section on how to make them yourself.
I personally haven't seen any ready-made connections with swivels being sold online - only the complete chux.