You could take a level of the hunter hybrid class. The hunter spell list includes all druid spells of levels 0-6 and all ranger spells. If a spell appears on both lists, the hunter treats the spell as the lower level. For example, Read Magic is a level 0 druid spell and a level 1 ranger spell, so it is a level 0 hunter spell. The hunter is a spontaneous caster. One level of hunter would get you Lead Blades, but you would need seven levels tp get Instant Enemy, a level 3 spell.
If you are not playing PFS, perhaps you and your GM could work out some sort of spell research.
I should have mentioned this.
Independent Research: A wizard can also research a spell independently, duplicating an existing spell or creating an entirely new one. The cost to research a new spell, and the time required, are left up to GM discretion, but it should probably take at least 1 week and cost at least 1,000 gp per level of the spell to be researched. This should also require a number of Spellcraft and Knowledge (arcana) checks.
Independent Research: A divine spellcaster can also research a spell independently, much as an arcane spellcaster can. Only the creator of such a spell can prepare and cast it, unless she decides to share it with others.
For that matter, Instant Enemy won't work on a normal Hunter either (still no Favored Enemy). You could go Hunter VMC Ranger to get Favored Enemy, but VMC Ranger is normally quite bad(*), and if you are actually a Druid instead of a Hunter, it still doesn't get Ranger spells onto your spell list.
(*)If you go with the Pelagic Hunter, Roof Runner, Scarab Stalker, or Verminous Hunter archetype, VMC Ranger gets better, since you are no longer duplicating Woodland Stride at higher levels, and with or without these archetypes, your Tracking will be insane, so be sure to get Skill Unlock (Survival) and eventually you'll actually have a decent shot at tracking things that leave no tracks. And since Instant Enemy is a 3rd level Ranger (and therefore Hunter) spell, it comes online at 7th level, just in time for Favored Enemy to come online from VMC Ranger, although the way I read Favored Enemy in VMC Ranger, its bonuses never go over +2, so it's still not great (although if you could find a magic item to boost it, then it would get better -- can't think of any off the top of my head, though).