For shield only 1 option for Necro :
Outcast Shield. and for Caster Weapon a Dead Sword wich allrdy has some green accents. (dead swords are pretty huge btw.)
Focus i use with my Necro and wich looks awesome to Obby Armor is: Pronged Fan
Scepter maybe a Dead Scepter or Serpent Scepter.
by dyeing with multiple colors (2x green 1x black 1x brown) or smthng u can try to color match each Main and Off hand weapon from the Green Shade.
!!!!This is pure esthetic and maybe not as usable because of Soul Reaping Attributes of the Wand and Offhand i suggested.!!!
for better Help we need your Attribute ( i assume Death since u mentioned the Skull-Focus).
Also an Effigy Focus can look super dope on a Necro and is very nice dyeable and can maybe combined with a Scepter of the forgotten