Many - as always, over every year/half-year/month.
It’s close to impossible to keep up-to-date with new indicators.
Even reading technical journals and websites inevitably has some built-in delay, partly connected with “who decides to publish what, and when”. By the time you can read about the newest ones, at least hundreds of other people already know about them. ([I]Many[/I] of them, of course, are worthless anyway - but not all … it requires a lot of education, judgment and experience to sort out what’s “real” and what’s potentially going to be useful to you.)
Books like this are frequently published (this one’s not new, but it’s just an example from when I was using indicators, myself), but they tend to be very expensive: https://www.amazon.co.uk/New-Frontiers-Technical-Analysis-Strategies/dp/1576603768 (that one, written/compiled by a senior technical analyst at Bloomberg, is rather interesting: it explains some new indicators from Erlanger Research which are still not on Phil Erlanger’s website).
Edited to add: don’t imagine that because of publication-speed, websites are going to be more up-to-date than traditionally published textbooks. [U]The opposite tends to apply[/U]. Partly because many established authors who are themselves successful, professional traders [B]don’t[/B] want their work to be published on the web (at least until they’ve sold some books!). The reality is that in “research fields”, quite often (in other subjects, too), the internet is some way [I][U]behind[/U][/I] traditional academic publishing.