These are not mine, not affiliated.
BG Micro has these toroid cores on sale, 30 cents is dirt cheap I think. I don't know how long the sale is for.
https://www.bgmicro.com/ferrite-torroid-core-emi-noise-filter-31mm-x-16mm-x-19mm.aspxFerrite Torroid Core EMI Noise Filter 31mm X 16mm X 19mm
Ferrico FT-5-31X16X19
31mm Diameter on Outside
16mm Thickness
19mm Diameter Inside
