(Insert obligatory "maid costumes are not lolita" comment)
Bodyline does have a few maid costumes with lower necklines. They don't have any lower-necked ones with the large shoulder frills, though, so hopefully you aren't too in love with that design element if you go with Bodyline. I would browse their maid section
to see what you like.
is a brand that makes maid costumes, but they tend to be a bit pricier. They have a large selection of styles, but prices run into the hundreds.
I think that a search for a maid costume would be better suited to a cosplay section of the forum than a lolita section, though.