The Valenwood DMV... But in Skyrim there are just not many of them around. Apart from random enemies, there are only two guaranteed hostile ones in the whole game. http://www.uesp.net/wiki/Skyrim:Orchendor http://www.uesp.net/wiki/Skyrim:Nimphaneth
Do you need them for Hermeus Mora quest? There's one persistent body in the cave below the Thalmor embassy, another one in the dwemer ruins where the entrance to Blackreach is located.
Many outdoor bandit camps have at least one wood elf archer. I think they are random, but you can try a place with lots of bandit archers like a fort ruin.
Outside and around the Falmore embasy, ive bumped into a few of what I think are Falmor scouts/ hunters, little woodelves attacked me on sight, may only be after the main quest involving this embassy though.
If you need the blood for Septimus' quest just go to Liar's Retreat: there is every type except for Altmer, but you can get that from any number of places (Northwatch Keep is one place you should/could find pretty early on).
Riverwood. There is a certain Bosmer that would be better off dead. *grumble*
I'd rather not kill him because I made him a blade, plus he was one of my companions in my early levels. I'll have a look at the Silent Moons Camp then for a wood elf to harvest it's blood.