I wouldn't necessarily go with products. Some more natural ways to do this would be to brush your teeth, and when doing that brush your tongue a little more than you usually do. Inch till you feel the gag coming on, but don't over do it. I never intended it, but by brushing my tongue so thoroughly through time, I weakened mine a lot.
Also, the angle of trying to deep throat is important to. Some positions are better than others. And always take a nice deep breath and relax before going down. Go at a slower pace, it should stave off the reflex.