Is there a possibility to find any necromancer robes better than the standard necromancer robes? Also im in search of a hood that would also match. I want to keep a necromancer outfit for my character but the 75% regen magick buff isnt enough

The types of robes you find are surprisingly weak. You might be able to disenchant one and then as your enchantment skills grow, create better ones. But I really don't know if that works. Even the Arch-Mage robes are weak. They look cool and they're certainly helpful, but they're not a corrolloary on the order of something as effective as ebony armor--which they should be. Not that they shold give you that armor rating but they should do more than they do.

As for finding them, I've rarely found better than Adept type robes at any level that I've reached (around 50).

I wouldn't pay much attention to magicka regen on robes since in combat magic regen is horrible which is when you really need the regen (unless the regen rate has been changed in a patch I'm not aware of) You're far better off enchanting your own stuff with fortify (magic school) that you prefer using and dropping your spell cost down rather than trying to focus on the actual magic regen itself.

As for the hood, I've never seen a hood that matches necromancer robes. The only hood I've seen is the one that thieves on the road wear when they try and rob you.