Penny becomes available after you complete a few quests for her. These open up after you've chosen the Lumber Mill at the Gorgrond outpost - not your personal garrison.
1.You will get Uncommon follower:Penny Clobberbottom.
2.You need to provide your account.
3.Your character needs to be lvl 94.
4.ETA:1day.
You will get Alexi Barov when finished Quest: The Rise and Fall of Barov Industries: Alexi Barov.
Alexi Barov is a horde follwer.
1.Related Garrisons building:Lumber Mill.
2.You will get Uncommon follower:Alexi Barov.
3.You need to provide your account.
4.Your character needs to be lvl 100.
5.ETA:1day.
Blook can be found in Blook's Overlook. There is a path to the right as you pass through the mountains from Gorgrand to Talador. If you climb to the top, you can fight Blook. And if you win Blook, you will join your garrison.
1.You will get Uncommon follower:Aknor Blook.
2.You need to provide your account.
3.Your character needs to be lvl 96.
4.ETA:1day.