Is there a way to gather materials for the Artemis Suit upgrades without combat?
Yes.
Suit Schematics, Health Monitors, Power Regulators and Manufacturing Instructions can all be obtained as mission rewards, including from mission types which don't require combat. They can all also be salvaged from surface POIs (usually without combat if you're quick, and you can always try a different one). Power Regulators can also be obtained by taking restore/reactivate missions and then abandoning the mission ... but it's often worth
doing these missions as it's a good opportunity to salvage the rest of the bits.
Aerogel and Graphene can be picked up from bases - you just need to either pick an inactive base or a time no-one is watching. You can also trade other materials at the bartender for them, though again you'll need to get those materials by quietly robbing bases.
All Odyssey materials can also be traded player-to-player.
If you're not actually playing a strict pacifist, you can extend your range of allowed surface missions to a wider range of restore missions, and also a few others involving abandoned/damaged bases, by carpet-bombing enemy scavengers with dumbfire missiles from your ship - technically combat, but no actual risk to you. If you
are playing a strict pacifist ... then you probably don't need an upgraded Artemis suit in the first place, at least not beyond what you can find in the shops - those plants don't bite.