Well i use Evermotion 3d models- they come in editions, one of them is only with vegetation- volume 7 i think. I download the models via torents and they come with a Pdf file overview that shows the contetnts of the model.
Please note that the models themselves are in high detail and that means a lot of geometry- so more than 4-5 models in the same scne will slow your computer. If you plan on using lots of models, i think Proxy is the way to go 🙂
Now i don-t use these 3d tree models unless i don’t have other choices- For saving time i render the image without the trees and then add PNG vegetation images in photoshop later. Of course it is not 3D but it saves a lot of rendering time:)