From amazon! Medium brown was perfect for me since it gets darker the longer you keep the tint on. Here’s the link:

https://www.amazon.com/dp/B000AS45LC/ref=cm_sw_r_sms_c_api_i_vDyqEb2DEZS65

Hi! I also struggle with my eyebrows, and I recently starting using something from Amazon called “Tint Kit” to dye the hairs I do have darker and then I leave it on a little extra time so it kind of temporarily dyes the skin under my brows. You have to be careful and apply it in increments so you don’t end up looking like Groucho Marx, but I’ve found it to be really helpful in boosting my confidence. I love to ski and my eyebrow pencil always comes off when I sweat or my hat rubs them causing me to be extremely self conscious, and this has turned out to be a good temporary solution :) you have to redo it every week or two to keep the pigment on your skin.

https://www.amazon.com/Godefroy-Professional-Medium-Brown-Count/dp/B000AS45LC