You can get basic support from the Repair NPC (Choose 2nd option from the initial question they ask you). Its the same support that is offered out at the camps. If you need Guild or Master support, then it does sorta make sense you need to go to those guilds. Eitherway, I've found very few synths worth leveling up on that you couldn't either A) grind through with proper books or crafting abilities. or B) level up on a different synth.