I see that you are missing various Swedish names, like Gudrun. I don't know if you can get the full list of names, but you can get the list of names which were given to at least 10 girls in the last decade or so at:
I don't have need for this data and I can't comment about the effectiveness of the API.
You can get top-1000 US names for a given year by going to http://www.ssa.gov/OACT/babynames/#ht=1 , selecting a year, change "Popularity" to "Top 1000" and submitting the form. (For example, your search doesn't have 'Lowell', which was #172 in the US in 1940.)
Thanks a lot. I'll look into this.
Regarding missing names. I'm adding around 10.000 profiles a day to the dataset. So it get's better by the minute :) Not that huge a dataset yet.