Where you find everything else.........Ebay
You could also probably use Spectra or Dyneema. Just make sure you have some sort of material between the Kevlar and your skin (ie. it'd be itchy).
Note that cutting things like Kevlar is super difficult.
Fun reading: Ultra-high-molecular-weight polyethylene - Wikipedia, the free encyclopedia
I *think* you can "cut" Spectra or Dyneema with a hot soldering iron. It might be the better option for patching. Dunno. Never used it--just heard my father-in-law talk about it in regards to sails.