It seems that these are called wave springs:
"A wave spring, also known as coiled wave spring or scrowave spring, is a spring made up of pre-hardened flat wire in a process called on-edge coiling, (also known as edge-winding). During this process, waves are added to give it a spring effect. The number of turns and waves can be easily adjusted to accommodate stronger force or meet specific requirements.
A wave spring has advantages over a traditional coiled spring or a washer:
Axial space can be reduced by up to 50%. As a result, the overall size of the assembly becomes smaller, reducing weight and production cost.
The load in an axial direction is 100% transferable.
One multi-turn wave spring replaces multiple stacked wave washers. This eases installation and reduces maintenance times.
A wave spring can accommodate higher thrust load within the axial space as only the wire size, number of waves, wave height and number of turns need to be adjusted to accommodate higher thrust loads."
Used replacements can be found on eBay or you can Google for new ones.