This drives me nuts. I love gettings vocals in but actually finding them without recording them yourself is a massive pain.
You can try to make them yourself though the results are usually pretty bad. Other people do it but usually it's pop music that gets the treatment and once again, they usually sound rubbish. There are also some websites but once again, they tend to be rubbish.
I guess you'll have to search for old disco accapellas like everybody used to do.

We still doing this?

That's some nice hip-hop. Listening at low volume right now but its sounding great to me at the moment.

Here's some of my favourite electronic albums

deadmau5 - Random Album Title
Roni Size/Reprazent - New Forms
Digital - The Archives
Frankie Knuckles - A New Reality
Massive Attack - Blue Lines
Nightmares on Wax - Smokers Delight
Daft Punk - Discovery