Are you selling a contract or trying to buy a contract?
DVC can provide information about what they require before a contract may be sold. They will still have Right-of-First-Refusal so any offer will need to be submitted to DVC prior to closing. A closing agent may be used without using a broker or much of the legal work can be done by the seller without the expense of a closing agent. Some sellers have also found their own buyer and then negotiated with a broker to complete the sale.
Just contact DVC for information about selling your contract.
Yes, possible locations include ebay, TUG, Timesharing today and redweeks among others. All the broker does is get the 2 sides together. It can save the buyer some money and it can net the seller a little extra, esp for high demand options.