It stinks that you have to run through the game again just for 1 achievement, Recon. I assume you're using the x360a.org quide. It is definitely not complete. From my experience, there are approximately 15 persuasion opportunities during the main quest, 20 in Factions and 40+ in side quests. There were at least 20 more chances to persuade after I hit 50 and unlocked the achievement. I'm not positive because I stopped keeping count.
For some help I'll tell you what I did. It should be a given but I maxed Persuasion as early as possible and saved before every quest-related conversation. If a persuasion opportunity isn't available from the start of a conversation, always select the left-side dialogs options first. Never choose the bottom-right (aggressive/dismissive) dialog option as it ends many conversations before they even give you the opportunity to persuade. There are only a handful of persuasions that appear after selecting the bottom right dialog. I can't remember them so it's not worth selecting it.