How to Get Google+ Invite
The workaround is simple to exploit and requires just two simple steps. Note that you, or someone you know, has to already have Google+ access in order for this work. There's also the possibility of Google plugging this hole pretty soon, so you'd better be quick.
1. Create a new circle (via circles tab at the top of the page) and add to it exclusively people with e-mail addresses who do not have Google+ access. You can add from one person to as many as you need to invite.
2. In your stream, share something (text, photo, link) solely with the new circle (must not be public) you just created and make sure you click the box saying "Also e-mail X person not yet using Google+"
After a few minutes (depending on Google's server load), each person you added in that circle will then receive an e-mail with the content you shared. After they click the link in the e-mail, they can sign up to the service with their Gmail addresses.
source : pcworld