I absolutely love rockabilly and retro clothing, and I've looked around a lot and found that most of it's not plus size too. And if it is usually the highest they go to is a (small) 2X or it's incredibly expensive...$70 for a simple pencil skirt, yeah right.
There are a few tutorials on here that I've found and will definetly be trying. And they're super easy, even for a sewing novice.
Simple Pencil skirt: http://www.craftster.org/forum/index.php?topic=35275.0
Pencil skirt with gathered darts: http://www.craftster.org/forum/index.php?topic=72797.0
Pencil skirt with pannels and back corseting: http://www.craftster.org/forum/index.php?topic=18314.0
Also Lip Service has some great looking outfits, and they usually show a drawing of each piece, so it's easy to figure out the patterns.
Or if you google "how to make a pencil skirt" a lot of different options come up, I've found that when I look for tutorials I need to be pretty specific.