I've tried everything to get Arcade Gannon to talk about the Enclave remnants, I'm idolized by the Followers of the Apocalypse and diverted the power from Helios One to Freeside, so what should I do?

What is your current story mission called?

For the Republic, Part 2

Okay, there's your problem. You have to finish that quest for him to talk about the Remnants.

You can't finish it. It's the final quest for the NCR, so you can't leave once it's begun.

Okay, well, that's what the strategy guide says you have to do. Maybe you can't do the Remnants quest if you follow the NCR path?

I'm not sure if I can help you anymore without actually going through he game and trying it myself.

That is untrue. One part of the Remnants quest is telling them to support NCR in the fight.