I reccomend Snover, Abomasnow.
Snover learns Grass whistle at lv 13 the same with Abomasnow.
You could also breed with Bulbasaur and Chikorita line but they must learn it by breeding too.
So get a male Snover/Abomasnow to lv 13 but if you have a abomasnow you could just get a heartscale and go to dendimelle. Then breed with a female Treeko/Grovyle/Sceptile.
Hope I helped