I had the same problem you have with sight-reading, and I tried to discipline myself and sight-read every day for an hour or so. It didn't work... However, now I am a Grad Student, so I had to do lots of accompanying for singers, clarinetists, etc. In just one semester my sight-reading has progressed immensely. If you have any chance, do lots of accompanying - not only you learn useful repertoire, but you also get to work with other musicians, understand phrasing, musical form, structure, etc. I cannot emphasize enough on this matter. Plus, all other instruments except piano need accompanists... and the clarinet pieces are hard as nothing else... especially the contemporary ones. So, start now with your Voice Major friends... do it for free, or smaller charge than other accompanyists at your school. Later on, you will be able to make it through graduate school just with accompanying.
The major principle in sight-reading is to allways keep focus and look one measure ahead. This is a matter of discipline, and that's why, when you play for a singer or another instrument, you have to keep playing, otherwize you have to stop...
Another thing that may help you, and I know it sounds a little dumb. If you have professional accompanists or really good sight-readers, go and watch them sight-read, or turn pages for them at recitals. This will help you look at the music, hear it, and see how it is being played all at once. It makes sight-reading look a bit easier.
Hope this helps. If you don't find music that you want at sheetmusicarchive.net, send me a message with your e-mail and the name of the work; I will most likely will have it.
Titus