I have read that you just show up. If they groove on your vibe you are welcomed. Otherwise, they encourage you to move along. It's a small place near the town of Orgiva. In Spain's Alpujarras region. (In the province of Grenada.) Beneficio: Orgiva’s hidden community of hippies and flower children Beneficio - Wikipedia
Have you tried the Spanish embassy, or probably better, the Spanish tourist board in your own country.? I believe that this agency has a lot of dealings with them. Their is an email address (but not a phone number) on their website. Beneficio community in Spain: an alternative trip - Voluntouring.org