Yeahh I sadly don't know of that many myself, in webcomics at least. Some misc examples of kinda-sorta:
This is a spin-off one-shot that seems to be a tournament of some sort (but said tournament has yet to begin:
Similarly, there seems to be a tournament coming up soon in this comic, but there's been chapters of char introductions so it's not there yet:
And this one I've started reading over on webtoons on someone else's recommendation. It's got small bits of tournament duels buried under heaps of BL xD
But it def seems to be a lacking trope in webcomics! (as opposed to like shonen manga where like 1 out of 3 series has a tournament at some point. Never change, battle shonen xD <3)
As it is, I'm in the process of writing a tournament series, but it wont be ready to start for some time @u@;;