There is a Costume Jewelry necklace I want, but it is gold and I need it in silver. Is there a way to change the color to silver? Maybe spray paint or a paint for jewelry? Thanks.

I don't know about changing a gold to silver. You can try to find a handcraft jewelry designer to see if they can 'replicate' the look to a similar design in the sterling silver metal.

Where can I sell costume jewelry? I saw it on an antiques roadshow once, where do I start to sell it?