Google is your best fried.
In the forum is a simlar question some time ago → Other pretrained models
But notice these models and corpus you will get are mainly a toy you can play with, actually far beyond any serious use.
The task you are interested (translate web pages) from scratch, with OpenNMT is a difficult task (very difficult indeed), not only because you have to deal not only the core translation (a whole problem by itself), but the real word (set a whole flow from the input web page to the output page, servers, file pipeline).
Humble opinion here, you should should select a more affordable task, for instance “learn” neuronal translations or how to setup a translation system for webpage. It depends a little bit of your interests,
Hope this helps!
Have a nice day