First, how exactly are you planning to ensure obtaining these team members? Nuzlocke teams simply can't be planned. Nevertheless, there are some solid Pokemon that are easier to obtain than others.
Any one of the starters is good. Grookey's line is good against Milo, Nessa, Gordie, and part of Raihan's team in terms of Gym Leaders. Scorbunny's line does well against Milo, Kabu, Opal, and Melony. Sobble's line performs solidly against Nessa, Kabu, Gordie, and Raihan.
If you can grab one, a Barraskewda sports a wide range of coverage moves, and its Attack and blistering Speed will make it a force to be reckoned with.
The gift Toxtricity from the Daycare is also helpful, as it can easily deal with Opal, and Electric is quite a good type to have in-game.
Excadrill can be good. While frail, it's very fast, and can hit very hard.
You can catch a Sizzlipede in the Motostoke Gym Challenge, which I strongly advise. Centiskorch is phenomenal in-game. It boasts a good set of moves, and can hit hard.
If you're playing Shield, get a Dracovish, preferably one with the Ability Strong Jaw. Seeing as you get it at Level 10, the levelling up may seem daunting, but Dracovish is worth it. It gets access to Crunch, Psychic Fangs, and the almighty Fishious Rend, the latter of which comes just in time for the battle against Leon. Couple this with weaknesses to only Dragon and Fairy types, and it should be clear why you should put a Dracovish on your team.
There are other good choices, but these are some of the easier ones to obtain. Hope I helped!
