There are a couple of figures on the very earliest years in the timeline in Web pioneer Kevin Hughes’ "From Webspace to Cyberspace,” attached.
After 1996, the Internet Archive is likely to have some accurate figures from their Web crawl.
Let me know offline if you want me to put you in touch with Kevin or folks at the Archive for further info/ideas.
You might also consider contacting ISOC or W3C.
Best, Marc