Come to the Colorado Aquarium Society Club meetings first Friday eve every month. There are scads of people who have plants and would sell plants, plus there is a mini auction every meeting with any assortment of kinds of plants and also fish.
4101 E Hampden Ave
at the First Universalist Church of Denver
Fun and worth the time every meeting. There is a separate Killi Club too if you like Killis and there are excellent breeders.