It's a drive, but Coin and Bullion reserve in PC is probably the most reliable and highest paying person.
If you're selling gold do not use one of the mail services you've seen on TV they are scams and will give you less than 20% of the value. If you've already done this and haven't cashed the check call them and tell them to send it back. They generally hold whatever you've sent for 30 days or the check is cashed.