@Xeux is correct, repairing your Gallente Faction standing won’t take long at all. In fact right now you have access to the Level 1 Gallente Data Center Agents that can give a real quick increase to Gallente Faction standing.
I’m not sure what you mean by saying “Already Spent”. There’s a lot of Agents listed in the ‘Faction Standing Repair Plan’ and it would help to know which Agents you’ve already completed.
Despite how it looks, it actually won’t take too long to repair Amarr and Caldari standing, just have to start with regular Level 1 Amarr Agents located in Minmatar space and complete a few Storyline missions until you get Amarr above -5.00 standing, then you can enter Amarr space and start working Amarr Agents listed in ‘The Plan’. Doing that will also raise Caldari standing as well and when Caldari is above -5.00 standing, you can then enter Caldari space and work Caldari Agents listed in ‘The Plan’.
I’m talking about the Career Agents, Circle Agents, Data Center Agents, Cosmos Agents and Epic Arc Agents. It doesn’t matter if a majority of those missions are just a one time deal, if worked correctly (as in switching back and forth between the Factions as needed) the amount of Faction standing increase they give is more than enough to make you positive to all Empire Factions.