You can get,
162 Colombo Bandaragama /Idangoda/ Matugama/ Bulathsinhala/Kalawana
(via Pettah > Fort > Lake house > Gamini Hall Junction > Town Hall > Independence Ave > Colombo Campus > Thummulla > Thimbirigasaya > Havlock City > Kirulapone > Kohuwala > Pepiliyana > Rattanapitiya > Boralesgamuwa > Piliyandala > Miriswaththa > Kesbawa > Makandana > Baduwandara > Kidelpitiya > Welmilla > Gammanpila > Bandaragama)
120 Colombo Piliyandala/Horana/Kesbewa
(Via Pettah > Fort > Lake house > Gamini Hall Junction > Town Hall > Independence Ave > Colombo Campus > Thummulla > Thimbirigasaya > Havlock City > Kirulapone > Kohuwala > Pepiliyana > Rattanapitiya > Boralesgamuwa > Piliyandala > Kesbawa > Kahatuduwa> Gonapala > Pokunuwita > Horana)
139 Kalubowila Piliyandala
There is only known bus stop no particular place to stop bus
And other hand you should stand on your leg because there's no hut or seat for passengers to untill waiting to bus
In my opinion, Sometimes bus delay and after 6.00pm horana 120 bus are very few
Following buses stops here
120 Pettah - Kesbewa
120 Colombo - Horana
162 Colombo - Bandaragama
139/1 Kalubowila Hospital - Piliyandala