Is it possible to obtain a specific sequence dance script without joining a 'club'?

The answer to that must be "it depends".

Many of the old dance scripts have been published on web sites or in sequence dance books.

Most of the newer scripts are only available from a few licensed publishers and I think these all require subscrion of some kind.

However, some of the societies publish their own competition winners in their member magazines which you may be able to find, and Dance Today magazine publishes some scripts, usually a few months after they first appear.