I taught myself to deepthroat using realistic dildos. I see you reviewed the Softee vibrating ballsy super cock 7"; that one could work. If you have a partner, of course practicing on him would be better. Make sure any dildo you use has a base that will prevent it from going in TOO deep and getting stuck, because that could be (fatally) bad!
The trick is to overcome your gag reflex by learning to relax your throat. It can be done with practice! Concentrate on relaxing as it starts to enter your throat. Remind yourself that you WANT it in your throat, and that it won't hurt you. Try to swallow the dildo (or penis). You can make it a little easier by applying some water-based lube to the dildo. Be patient and practice daily; you WILL get good at it.