Are you looking for references of finite elements? the Grad-Shafranov equation? or specifically using finite elements to solve the Grad-Shafranov equation?
I would suggest looking into:
Gruber, Iacono, and Troyon Journal of Computational Physics 1987
K. Lackner Computer Physics Communications 12, 1976
J Blum, J Le Foll and B Thooris Computer Physics Communications 24, 1981
J.L. Johnson Journal of Computational Physics 32, 1979
Some of these papers deal specifically with finite elements, others are review papers of numerical methods used to solve the Grad-Shafranov equation.
You might also look into Stephen Jardin's book: Computational Methods in Plasma Physics
I've written a spectral element code that solves the GS equation, and can probably answer any specific questions you have.