As far as I know, it is only possible to build 2 hippy communes. As far as building up to the brick yard is concerned, anyway.
In order to get a third you need to capture one from the enemy AI, which is fairly straight forward. Obviously it's better to wait until the enemy AI is ready to build their brickyard before attempting to capture their hippy commune. I would suggest moving an entire work team over to their commune, rather than just the foreman, this way you can use the builders as defense while your foreman takes down the communes fence. The enemy will usually respond by sending in its own builders , so initiate fisty cuffs on them by using your own builders.
Once the fence is down, repair it. The AI will occasionally send in a foreman to try and take it back. Now you're ready to picket 3 resources, so
save your game. I would start by selecting hippy communes furthest away, select the picket icon and hit
to purchase. Then select the resource. Do this twice more from each commune, selecting a different resource each time.
Now this will still require an element of luck. No doubt the enemy will have police patrolling the estates, but I managed to get this on my second attempt as the hippies only need to all be at the entrance of the yards at the same time for this to count.