Where can you find their fossils today?

Bothriolepis from Escuminac Bay, Quebec;
courtesy of the Canadian Museum of Nature.
Photo by Annetta Markussen-Brown
The world's best-preserved placoderms come from Australia such as the Gogo and Christmas Creek Formations. The Gogo Formation represents the quiet deeper waters away from high-energy reef fronts. The great diversity of fishes found in these deposits are excellently preserved because of the lack of later geological activity that kept the region free of large crustal movements which usually deform and compress fossils of this age. Placoderm fossils are also notably found in the Old Red Sandstone outcrops of Scotland. 
In Canada placoderm fossils have been found in marine deposits of the Escuminac Formation of Miguasha, Quebec.