There are a couple of ways that you can achieve this.
The primary way is to create the need for it. Using the JME forum, create interesting topics involving the blackberry, and try to get people involved. After a while others will also use the forum for blackberry questions, which you can help by answering (or help with research) the questions. Once the forum gets its share of blackberry related questions, and there is a need to spin it off from the JME forum, it will likely be done.
An alternative way, which has been done in the past, is to do the book promotion route. With a couple of blackberry books in the pipeline, a new forum could be created. Maybe you can help with some recommendations (books and publishers)?