You can't really do much besides practicing the pattern. There aren't really any handstream-specific packs, mostly you can find them in same packs that contain JS stuff (on etterna, some of the most common ones are Nuclear Blast JS, Icy X, Elexon, Jumpstream of fighters, Overloading stamina training), if you don't play etterna you can find most of them in tachyon's etterna conversions post. Also the user above actually suggested you a chordjack pack, I don't remember a single JS/HS chart in it. Maybe they got confused by some older etterna ver (older calcs might calculate some CJ charts as HS charts). Tech is a completely different thing by the way, and it's very reading-dependent because, well, anything can happen in a tech chart.
I've been pretty bad at anything dense (mostly HS and dense JS like icyworld's WLL or Elekton's A) for a long time too, both because of my playstyle (playing with wrists up makes it kinda uncomfortable for me to hit something so dense and fast consistently) and reading (self-explanatory, I'm really inconsistent at these patterns and find normal streams way simpler). And usually I don't even like the music in these kinds of charts, so I didn't bother. But more recently it was actually fairly easy for me to get it to an acceptable level at least, just by playing denser stuff for some time. Besides practice, I'd suggest to try starting with more streamy/trilly JS files (like the easier diffs of icyworld's Gate Openerz or WLL) and try visually separating the chords from single notes. I'm pretty sure it won't be hard to understand the pattern. After practicing simpler ones you should be able to move on as long as you have enough speed and stamina.