Best stores for Bettas and plants?

I'm in the Los Angeles area. I researched betta fish heavily when getting one for my daughter earlier this year, and for some reason it didn't even survive 6 months. I worry that I either got a bad fish or bad plants that had a harmful bacteria - I know the water was balanced/healthy and nothing else was done wrong, so I can't figure out what else could have been the issue.

To that point, I'm wondering if anyone has suggestions of local (Los Angeles) or online stores that are good for plants and fish. And suggestions of good varietals of plants are also welcome. Hoping things go better this time around. Thanks in advance!