Most schools provide the option of entering either Masters or PhD program in Economics to prospective students with Bachelors degree because both are considered terminal degrees.
As Stiffler suggested, you can easily do the search online. Here's one helpful link:
http://grad-schools.usnews.rankingsandreviews.com/best-graduate-schools/top-humanities-schools/economics-rankings
From there, you can further drill down to the schools' Economics Department website. Depending on the concentration within Economics that you are interested in (such as Econometrics, Monetary. Labor, etcetera), choose the schools you want to apply to.
Furthermore, as I suggested earlier, look at the faculties and read their publications. Since your GA-ship depends on your advisor (your key professor), you should know his field and show commitment to work in that area.
If the admissions committee sees you as a promising doctoral candidate, the funding should not be a problem, especially in larger programs.
Grad school is no joke, especially in reputable schools. Not many can crack it. In that vein, let me share an anecdote. Here's what one of my old profs said to our incoming class:
If you graduate with distinction, you will start a grueling career as an assistant professor or post-doc at a research university and earn probably $50K/year.
If you were an intermediate student, you will have somewhat easier career as a professor or lecturer at a teaching university and probably earn $75K/year.
If you were a mediocre student and still manage to graduate, you will get a job in industry such as Goldman Sachs or Chase and earn $150K/year.
Got the point?
Good luck! Gambatte Kudasai.
