I need help getting power cells for the air speeder. I already helped the merchant with the power cells leave and helped the family leave with him. He's gone now.

 

Where else would I get some?

You probably want to direct your question to the Spoilers section.

I am having the same problem....

Well, this deserves to be in the spoilers section (use the spoiler tags otherwise), but...

 

 

If the alien with the power cells left already, you're out of luck, unless there's another cell in the area which I don't know about. You had to ask him for a power cell as a reward when taking the mission. This possibly requires high Awareness.