I sure love Bortkiewicz piano concerto #1
And here is his page on IMSLP http://imslp.org/wiki/Category:Bortkiew ... duardovich
One can find lots of scores of his there.
As far as legality, given the recent issues IMSLP had with Universal and other publishers(back in 2006 or was it 2007), I don't think they would be posting music not in the public domain. Also, IMSLP is posting the following disclaimer:
"Works of this composer are most likely not public domain within the EU and in those countries where the copyright term is life+70 years. They may also be protected by copyright in the USA, unless published before 1923, in which case they are PD there as well. However, this composer's works are public domain in Canada (where IMSLP is hosted), and in other countries where the copyright term is life+50 years.
IMSLP does not assume any sort of legal responsibility or liability for the consequences of downloading files that are not in the public domain in your country."