Do you mean a sweet blackberry "brandy" which is really a blackberry liqueur? Or a real blackberry brandy which is dry and high alcohol, more of an Eau de Vie?
If you want the sweet liqueur try Clear Creek's, it was just released this month and is truly excellent.
Otherwise Leroux is one of the better ones, but get the one labeled Jezynowka "Made specially to the Polish taste", I have heard that it is the best one they make.
If you want the dry kind I don't know of any but Clear Creek makes a raspberry Eau de Vie