Couple years ago I was really doing some homework trying to find a suitable replacement wave spring for my pump mag. I thought the Smalley springs were a little too brittle and only really worked well with a beat up main spring.
What I found was Lee Spring, and their Redux Wave Springs. They're made from Stainless Steel and feature an additional half wave per turn vs. the Smalley wave springs that are suggested on the Tech Rat's Nest. I've found them to be much more reliable and have no issue functioning with a strong/new Gold Main Spring.
Part number is LW 100 18 0250S. Minimum QTY was 10 @ $6.00 a piece when I purchased mine a few years ago. Check out leespring.com
Hope this information is helpful to you maggots!