Friend of the Followers

Friend of the Followers is an unmarked quest in Fallout: New Vegas.

Detailed walkthrough
When talking for the first time with Julie Farkas about Freeside, she will tell the Courier that the Followers of the Apocalypse need a constant supplier for some ingredients used to manufacture medicine items.

For a constant supply, talk to James Garret at the Atomic Wrangler and convince him to strike a deal with the Followers. Then report back to Julie, convincing her that the Garrets want to help Freeside in exchange of the Followers' technical skills. After talking to her, report again to James Garret and he will inform the player character that some of the supplies will be sent immediately. Return again to Julie and gain a huge boost of reputation with the Followers.

The player character will also have to spare some of their own Med-X, RadAway or Fixer, 10 packs of one type will do the trick. Note that 10 donations of each are not required, but a donation of 9 (in 3 sets of 3) of one type gets bonus fame with the Followers. The first time you donate the 10th chem of one type, she will sell extra magazines (see below). (One can donate only Med-X for example, which is far more common than Fixer and RadAway.)

One can know the quest is completed when the next time they want to donate some supplies, Julie tells them that the item in question is already being mass-produced, but she will accept it anyway. After the donation, she will offer a discount in medical services and some magazines for sale (several Programmer's Digest and Today's Physician, some Lad's Life, Salesman Weekly and one Meeting People). The Courier will gain more reputation with the Followers as well.

If you exit dialogue and talk to her again to donate more while idolized (through quests or more donations) and  the extra magazines are unlocked, that will trigger the invitation to join the followers, as well as a discount if you didn't get that from High Times already.