I just ordered them off Amazon! Did a quick search and there were a bunch of options. I got a 150 pack and it came with the 3 rings too. I’m glad I got clear plastic as opposed to white because I can kind of hold the toppers over a color to get a better idea of how it will look.

Edit found it:

150 Pcs Clear Nail Swatch Sticks with Ring, Fan Shape Nail Art Polish Display Tips, False Nail Sample Sticks, Nail Practice Color Display, Transparent Polish Board for Nail https://www.amazon.com/dp/B089T2LSJ8/ref=cm_sw_r_cp_api_glt_fabc_V91SQXHB5JJTPV52D9K9