Here are a few suggestions:

1) Do a google search for 'sony headphones wh1000xm4 replacement plastics'

2) SONY Replacement Parts Website (what they offer) I found at this site.

3) Joe's SONY WH-1000XM4 Repair Parts I found at this site.

- The individual part you needed is offered along with a replacement metal clip.⏎

4) Check eBay - Currently (2/9/24) I see the part you need along with the two piece that attaches from the swivel joint to the speaker for about $11.99 USD

What you are describing as a ground spring could be better described as a eject spring. When you depress the battery latch it releases the battery and the eject spring pushes the battery tray/rechargeable pack out so you can remove it out of the battery compartment.

You should add additional photos of the MessagePad 2000/2100 Flip Cover with it in its closed position and with it in its open position with the Flip a cover locked in place on the back of the Newton. With it in the closed position you can describe how to open the Flip Cover which is by sliding the latch o. The right of the Newton behind the thumb in your current photograph. In addition you can show the back of the Newton where there are two clips positioned to hold he Flip Cover in its open position. Based on your Step 28 photo you are missing one of the two plastic clips.

The OEM Newton Stylus, which is replaced by a custom Black Aluminum Stylus here is stored in the Stylus Silo. It is held in place with a spring loaded lock mechanism. To get your stylus out you depress the head of the stylus which will release the locking mechanism and eject the stylus out of the silo a bit so you can grab and pull it out. When you store he stylus you press the head of the stylus in to lock it in place.