You can buy any DVC resort directly from Disney, whether you are buying in for the first time or are already a member and want to add on. The latest prices for the "sold out" resorts at WDW are $95/pt for BCV, BWV and VWL and $92/pt for OKW. I'm not sure about the prices at VB and HHI. The minimum purchase when adding on is 25 points if paying cash or 50 if you want to finance. There are no closing costs when adding on. You get full current-year points and pay dues pro-rated from the date you get your points.
Call your guide and tell him/her you want to add on at BCV or BWV (whichever you decide you want) and how many points you want to purchase. Disney will only sell you points in the same Use Year as your SSR contract. If they have points available, you give them your CC number and the points will be in your account within 24 hours. If they don't the have the points available, they will put your name on a waiting list. If you want BCV, it could take a few months to get the points. If you want BWV, you will either get them immediately or within a few weeks or absolute worse case a couple of months.
If you want BCV, call your guide and get your name on the list. If you want a "Plan B", then you should also contact The Timeshare Store and tell them you would like to buy a small contract at BCV and tell them your Use Year. Purchasing the same Use Year will allow you to have Disney set up your BCV contract as an "add on" to your SSR master and that makes it easier to manage your points. And keep an eye on TTS's listings just in case something comes up and they haven't managed to reach you by phone.
Good luck!