Is there any way to get both sets of unique weapons the AntAgonizer and Mechanist?
Yes. It involves reverse pickpocketing and then killing each one after they give you the weapons.
This method will get you both the Ant Sting and the Protectron's Gaze, as well as both costumes and an extra helmet for each one. This also gets you some bad karma, but nothing that can't be easily fixed with donations to churches or water beggars. You will need two sets of armor with a DR above 12 and two sets of headwear with a DR above 4.
Go to the Mechanist and talk to him. Do not convince him to give up his ways or agree to help him. Reverse pickpocket a set of armor and headwear on him, then leave and come back. His attire will change and you will be able to pickpocket his special armor and helmet.
Go to the Antagonizer and talk to her. Be sure to drop the Mechanist's armor and helmet before speaking to her. Do the same thing as before and reverse pickpocket the other set of armor and headwear. When she puts it on, you will be able to pickpocket her special armor and helmet as well.
Pick up the Mechanist's armor but leave the helmet where it is. Talk to the Antagonizer and give her the armor. She will reward you with the Ant's Sting. She will leave to wander the wastes. You MUST kill the Antagonizer in order to complete the quest at this point. When you loot her body, you will find the Mechanist's armor with an extra helmet to go along with it.
Go back to the Mechanist with the Antagonizer's armor in your inventory. Give him the armor and he will reward you with the Protectron's Gaze. Kill the Mechanist and retrieve the Antagonizer's armor with an extra helmet. -OR- if you want him to live; drop the helmet before you talk to him, then give him the armor and retrieve the Protectron's Gaze, then simply pickpocket the armor and extra helmet from him. Talk to Uncle Roe at Canterbury Commons to complete the quest.
If you have already have the achievment for the Quest, you can opt to just pickpocket them both with the methods above for both reward weapons, armors, and x2 copies of each helmet. This leaves the quest incomplete, but supplies a random encounter for the capitol wasteland with the Antagonizer (perhaps the Mechanist as well?) at a later time.
http://fallout.wikia.com/wiki/Talk:The_Superhuman_Gambit#Receiving_both_rewards_and_both_costumes