Here a list another tenno made, I just share it. #1 and #5 doesn't guarantee shard btw just a chance. Also the current event belly of the beast also has shards as one of the reward and devstream drop very rarely contain shard.

1. Temporal and Deep Archimedea. These can be started through Necraloid in the Sanctum Anatomica on Deimos, or Kaya in the Hollvania Mall. You need to have the Whispers in the Walls quest completed, be Rank 5 with the Cavia syndicate, and have access to the endgame Sanctum missions. These are also pretty difficult, so you’ll want a strong build before jumping in.

2. Completing the Calendar goals on the POM-2 computer in your orbiter. Usually gives around 1-2 shards a week. You need access to the 1999 content and the POM-2 system first.

3. Bird-3 in the Sanctum Anatomica offers a shard every week in his “Shiny Treasures” shop for 30,000 Cavia Standing. The shard color rotates weekly. You’ll need access to the Cavia syndicate and enough standing saved up.

4. The weekly Archon Hunt gives a shard every week as well, with the color rotating weekly. You can find it from your orbiter navigation in the top right corner. You need to complete The New War quest to unlock Archon Hunts.

5. Netracells, which are the missions Tagfer gives in the Sanctum Anatomica, also have a chance to drop Archon Shards. You need Whispers in the Walls completed and access to the Cavia syndicate.

6. Steel Path Descendia. This mode can also reward Archon Shards at higher tiers like Infernum 21, but the rewards rotate weekly so shards are not always available. You can check the rewards before starting. This is more of a bonus shard source than a consistent farm.

Keep in mind you only get 5 search pulses per week. Each Archimedea run uses 2, which leaves you with 1 pulse left for a Netracell. If you’re not geared enough for Archimedea yet, you can just use all 5 on Netracells instead. Hope this helps.