There are a number of US online retailers that carry both SE and injector blades. Connaught Shaving is the only UK based retailer that I have dealt with who carries SE and injector blades.
Here are some links:
http://shavetools.com/20ct-Personna-Injector-Blades.html
http://shavetools.com/10ct-gem-carbon-steel-se-blades.html
http://shavetools.com/10ct-gem-ptfe-single-edge-blades.html
http://www.uniquephoto.com/page-5--shaving-eye-care/gem-single-edge-blade-5-pack-9681/
http://www.foodotc.com/ProductDetails.asp?ProductCode=CN1047745&Click=6
http://www.razorsdirect.com/page/page/637542.htm
http://www.razorsdirect.com/singleedge.html
http://www.connaughtshaving.com/injectorblades.html
http://www.connaughtshaving.com/gemss.html