Since we are not sure what year the first Good Friday happened on, there is no way of knowing what day of the month it was. 13 being considered unlucky does not just apply to Friday's

With Easter itself being a variable day in between March 22 & April 25, Good Friday does not regularly fall on any date, much less the 13th. I found a table of Easters 1900-2089. Easter is on April 15 (Good Friday 13) 8 times in that time period. 1900, 1906, 1979, 1990, 2001, 2063, 2074, 2085. All you superstitious folks can relax now for 62 years & if you're still aroung then, rejoice! :-)