Resale does not qualify for internal exchange program. Even eligible members are not guaranteed success. If I remember correctly it is done lottery style. You put in your requests and since only a small percentage of owners in one of the non timeshare properties desire exchanges into the 2 timeshare properties, then the number is determined by the demand. Platinum owners probably have a better chance. I doubt the number fulfilled vs demand is greater than 20%.
I believe if you buy a unit from the association you may be eligible for internal retrades but I don't think the association will sell you one of their resales unless you already own at least one unit which could be resale or retail.
Straight out resale owners must use II or may be able to use RCI registry collection. I no longer own their and my info is about 3 years old but there is enough competition for the non timeshare property exchanges that I can't believe they would invite in additional resale purchasers to make the competition even more difficult.