I think you can get them from pretty much anywhere - more likely shops where older teens/students go like Topshop (there's probably other places like boohoo but I know they definitely do them!). And I don't think they're too slutty if they're worn right.
If you're worried about it looking like a bra, a printed bralet looks best and I think they don't look as slutty on those with smaller busts. If you want to wear a lace one, DON'T wear lace on the bottom.
To cover up a bit if you want to wear a fitted bottom like high waisted shorts or a pencil either cover your shoulders with a leather jacket or a blazer. Or, cover your legs, with a longer pencil skirt or a maxi skirt.
If its a hotter day or you can get away with less clothing (like a festival or something), team it with an a-line skater skirt above the knee that completely matches or in contrasting colours/patterns.
Another idea would be to wear it with high waisted jeans or trousers with a jacket for an alternative going out look. They look good with high waisted anything.