The instance of first JFrame is always available to you in the same class as this
public class CotizacionGUI extends javax.swing.JFrame{
public CotizacionGUI() {
initComponents();
}
private void buttonCallFrame2ActionPerformed(java.awt.event.ActionEvent evt) {
BuscarCotizacionGUI bC = new BuscarCotizacionGUI(this);
bC.setVisible();
}
}
Hope this is what you are looking for.
Good luck.