RCI doesn't allow you to sell points. People do it. I have seen them advertised on both the ebay (infrequently) and tug marketplace (infrequently). Points generally have a value of 0.009-0.01 per point when there is plenty of time until the expire. The closer they are to expiration the less they are worth. You also have to keep in mind use year both yours and the person that you transfer them to. You are allowed to transfer to another rci points account 1 time per year with no fee if you have a regular rci account and there is a fee for subsequent transfers. Platinum members can transfer multiple times with no fee.
So no good place to advertise since it is against the rules. Best to try to quietly find someone that you can make a deal with privately.
If on the other hand you are trying to sell/give away your whole timeshare then the answer is different.