Here's a site with a product that does this, but the design looks pretty simple to duplicate.
I use a simpler version that seems to work fine and you can use the pin as either. It kind of looks like a V with loops at the top of the V on both sides and a loop at the bottom of the V. The two loops go over the pin shaft and you close the pin and the chain or jump ring or bail goes through the loop at the bottom of the V. Hard describe. Essentially you're turning the V upside down.
Here's a site with another idea Haven't tried the drinking straw!
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pin-pendant by: Arsonhorse
You could try ebay, newmooncreations.com or google pin/pendant converter.
