I am not a native of a Spanish speaking country but lived in one for several years.
In all my time in Chile I don´t recall meeting anyone with the last name Magistrado. Also doing a search in google for "apellido Magistrado" came up with few results but I did find a page that may be useful that claims that the last name is from Italy. I have not verified the authenticity of the site but here it is(it´s in Spanish):
http://www.heraldrysinstitute.com/co...40994/lang/es/