Any more? I find the best way to search for mainstream porn with this plot is to go to porn sites, sort by milf, or new, or click on "sites" (if they have any that are directly about this theme. For example clicking sites in NaughtyAmerica then going to MyFriend'sHotMom, or BigCockBully/Thundercock - which it got re-branded to). The plan of attack I usually do when scouring the web for new mainstream of this sort is the following:
Brazzers: Brazzers Extras, MilfslikeitBig, MommysgotBoobs
NaughtyAmerica: Myfriendshotmom, Bigcockbully/Thundercock, MrsCreampie.
Bangbros: Sort by new, and look for videos that seem to have this theme, click on them, then read the descriptions to make sure I guessed right.
Realityking: The same as above
FilthyKings: The same as above
Fakings: The same as above. Though I will also click on the milf/mature tag, and whatnot, and look that way too.
SEXMEX: Same as Fakings.
Then finally I got to torrent trackers and search for keywords like: Mom, Son, Mother, Friend, Classmate, etc... sort by new, and sort through that way.
This is how I have found to have success. Because the western porn market is so divided.