You can indeed sell a copy of a master work. Generally the rule of thumb is any artist that is still alive or lived within the last 75 years is out of bounds. The seventy five years is to easily clear general U.S. copyright restrictions, and copying the work of a living artist and selling it is....well, tacky.
It is good to size your copy at least 5% off the size of the master work. I never sign the other artist's name but sign my own name instead and put "After" and then the original artist's name in regular script (not trying to duplicate their signature). It is also a very good idea to give credit for the copy on the back of the work and anywhere you use it for print or advertising, etc.
Competitions for master copies are probably pretty non-existent since they are derivative works and are most often done by students as part of the learning process - hence, not much interest and probably a slight disdain for such things in the art community as they are not
original works and thereby are not a true testament to the artist's actual proficiency.
But you can sell them, so take some comfort there.
