I have purchased these braided leashes many years ago from someone who used to make them. Does anyone know where I can find and purchase more.

Alex, what is the material? Those look cotton, not nylon but helps to know which.

This person on Etsy has a lot of variety
https://www.etsy.com/listing/108893703/paracord-leash

this round one looks similar: https://www.etsy.com/listing/167269676/4-strand-round-braid-paracord-leash?ref=related-3

These fleece ones look interesting.. you can totally design your own from colors to snaps!
https://www.etsy.com/listing/172328771/custom-order-fleece-braided-design-a?ref=shop_home_feat_1

I had braided cord for my horses, not dogs so no personal experience. Hopefully someone else here does.