SQL & PL/SQL

Hello all, I use Jdeveloper 11g R1 and have the following problem

I have a simple select query inside my view

SELECT 
    Opcine.SIFRA_OPCINA, 
    Opcine.NAZIV, 
    Opcine.SIFRA_KANTON, 
    Opcine.RACUN_JAVNIH_PRIHODA, 
    Kantoni.NAZIV NazivKantona, 
    Entitet.NAZIV NazivEntiteta 
FROM 
    OPCINE Opcine, 
    KANTONI Kantoni, 
    ENTITET Entitet
WHERE 
    Opcine.SIFRA_KANTON = Kantoni.SIFRA_KANTON AND Kantoni.SIFRA_ENTITET = Entitet.SIFRA_ENTITET

What I want is to just add a comma (,) for the results NAZIV, (It's kinda like County, City, State so all three are name).

So in the results I want it to be

Washington, Virginia, USA

Instead of

Washington Virginia USA

I tried the LISTAGG and WM_CONCAT functions but without using group by (as I don't want that) and it didn't work.

I also tried this ||', '|| but that also did not work, this is really what I want to use but without going all PL/SQL on it (wanna keep it simple).

Hope u guys can help