These might be obvious already (and hence redundant), but many computer history museums have sections covering software and programming language history.

http://www.computerhistory.org/

https://en.wikipedia.org/wiki/Computer_History_Museum

https://en.wikipedia.org/wiki/History_of_computing

Also try the Internet Archive (archive.org). It has a lot of "Programming History" stuff, but finding it can be painful:

https://archive.org/details/Kfest2011-PeterNeubaueLogoHistor...