I have had success nebulizing 2 vials (4cc each) of 7% saline to increase what I cough up. To deal with the oropharyngeal contamination, I keep start with 2 glasses in front of me, one empty and one with sterile water. Before I cough each time, I rinse my mouth with the sterile water and spit in the other glass. This routine has gotten me acceptable samples. I was intimidated for a long time by the requirement for submitting at least 5 cc, but I found that if the sample was good quality, they would process a smaller sample.
Good luck!