Wotcha dude and welcome and all that...
There's a book called 'Standing Stones; Stonehenge, Carnac and the World of Megaliths' by Jean-Pierre Mohen which has got loads of art stuff like paintings and old antiquarian engravings etc. It'a a bit of a tiny book but there's loads in it.
Also John Mitchell's 'Megalthomania' has loads of old drawings etc. too.
Hope this is useful,

Spaceship Mark.