You can buy the original art works at Konstantin Sterkhov's on-line art gallery. If you order an author's copy of an original art work you have to be aware that it is an author's interpretation that can be different from the original art work. But there are also advantages such as option to order your desired size or changing some details according to your idea.
You can contact Konstantin Sterkhov for a price and details
via e-mail: firstname.lastname@example.org
+7 911 725 4533
+7 812 455 3703