I have one and I use my own seeds with generic substrate sponges. They’re basically triangular sponges of peat type stuff, lots of generic options if you do a search.

I reuse my original seed pod baskets but if you don’t have yours you can either buy 3D printed ones on places like Etsy, or you can buy a single seed kit from aerogarden then reuse the baskets and little plastic covers in the future. It’s usually pretty easy to pull the plant out of the basket when you’re ready to start a new batch. For the cover I just use tin foil and punch a hole with a pen.

Idk where you’re located but I like buying my seeds from Renee’s Garden (search for “cut and come again container” to help narrow down). I’ve done various lettuces, herbs, and green beans successfully. I mostly use mine for lettuce type stuff.