Valorant's beta access will be handled through Twitch Drops and while the original plan was to kick the featured streams off on 7 April 2020, it now appears that an event will be broadcast on 3 April 2020 and it might feature beta access.
Several people who had access to Valorant over the course of the first full weekend in March 2020 stated that the game feels much more like CS:GO than Overwatch and other comparisons. Their insight apparently came from a Twitch Rivals tournament that was held during the same weekend but there is an embargo on the recorded content, which will be lifted on Friday, 3 April 2020.
Some of the most popular streamers from several streaming platforms participated but only those who stream on Twitch will have the drops with beta access enabled. Therefore, some streamers like Shroud will apparently not have Twitch drops or any kind of means to provide beta access, even though he is one of the best-known streamers in the FPS genre.
The most viable source of the full list of featured streamers so far appears to be Liquidpedia but keep in mind that the list you see may not be complete at the time you check the link. At the time of writing, the list contained the names of 99 streamers but Dr DisRespect wasn't one. Their streaming platform is displayed next to the name.
Those with the Twitch logo are most likely to have the Twitch Drops enabled so your best bet of getting access is by watching one of them on 3 April 2020.
Another important thing to keep in mind is that Riot Games did not officially confirm that the 3 April streams will have Twitch Drops enabled by the time this was written. Make sure you check whether the streamer of your choice has the feature enabled if you are watching before 7 April 2020.