M500BY

god, i must be really thick, either that or its too late at night. looked through previous threads on removal and replacement of double din stereo, but haven't managed to figure it out. anyone able to help me.
currently have a 1998 wrx fitted with double din sony unit. wish to remove this and replace with single din unit. whats my options for facia fittings and where will i get them? my dash colour is a dark grey.
is it acually worth trying to sell my double din size unit, and is there any demand for these or should i bin it?
thanks in advance, martin mitchell