Hey,
Hope this helps I personally have had success with this site
https://romsfun.com/roms/xbox
There is also Vimms lair which has some good ones ive not found elsewhere thats on https://vimm.net/
The download is an iso so i use xdvd Mulleter to extract the iso and ftp it over to my xbox also not sure what difference it makes but I have adblocker not sure what the ads are like so to be sure if you dont already id visit with an adblocker to be safe
Hoping this is allowed Im kinda new but im guessing it is ok if other folk are giving their sites too, Hope it helped