Gary's right, I left out Plastruct--and I even use their liquid cement!
He's also got a good point, in mentioning model railroading. I'd check for a LHS (local hobby shop), including a store that advertizes specifically as a model railroad supplier, as well as more general hobby stores. For me, Hobbytown is the LHS, and I think I may have the same issues with them as Gary does, but they do carry both Plastruct and Evergreen.
For L-shaped brackets, I'd use square styrene bar stock, with a model cement on the plastic, and CA glue to attach the finished pieces to the model.
As an aside, my issue with Hobbytown is that they don't have on hand the things you need, once you progress beyond a certain basic level. They can order some things, but even then, they don't carry some things in their catalog. Gunze-Sangyo paints, for example, or Vallejo or Andrea acrylics. But I have found that my local HT's owner is very willing to listen to requests, and he'll try adding new products, if a couple people ask for them. But generally, they're a sort of McDonald's or USAToday of hobby stores-a generic assortment of things aimed at the broadest possible market.
Please keep us informed on your progress, maybe post some pics as a step-by-step on how you build the skirts.
Prost!
Brad