Yes the usual situation is that renters in Sacramento come unrepresented. If you buy a house, you have the choice to have an agent that represents you, but is paid by the seller
If you want an agent to represent you (instead of one that works exclusively for the landlord) to find and negotiate a residential rental, you will likely have to pay for that yourself.
Because very few rental house hunters want to pay for this service, very few practitioners offer it. If available rental homes become scarce for an extended period of time, more agents would begin to offer a tenant paid service.
Generally you go to each property manager that represents the landlord- the inventory is not shared between property managers, a little different than the home buying process where you have your real estate agent and they have access to all the homes listed (not just their inventory)
When you visit the rental section of Trulia look for the contact information or link to the property managers website for showing and rental info. Most property managers have a website listing all their current available properties.