Piece of cake, but this is for profile not page.
Find a popular person in your niche, make sure they get some engagement and they're always posting fresh content. Then follow everyone who has that person in their circles. The limit for Google+ is 200 follows a day, don't worry about being banned Google will let you know if you've reached 200.
You keep doing that everyday and you will get people adding you back. Make sure no one sees who you have in your circles so that they don't see you as a spammer or someone who just wants more followers.
The limit is 5000 on Google plus, just like on facebook. Once you've reached your limit you can use Circloscope to unfollow everyone who doesn't follow back and repeat the process.
Make sure your account is frequently updated with fresh content, that will increase the number of followers.
Another way is to engage in communities (groups), find active communities in your niche and provide some value and people will add you to their circles. G+ communities are really powerful and less spammy as compared to facebook and linkedin groups.
It's that simple, but it will take some time and effort. It won't be fast but it works.
