I just go through amazon. I started out with variety/scrap packs (mostly Evergreen), which came with a bunch of great stuff to fill out the toolkit, then I bought more of what I ended up using.

https://www.amazon.com/gp/product/B00MR5EIN6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B0006O5FAK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B0006O5I20/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Awesome! I have made a ton of things like these in my workshop as well. If you want to print the bottoms, good on you. I am very impatient. So when I print larges things like this, I actually just print those walls, then glue them to a thin sheet of plasticard. There is NO way you can go without the bottoms on something like this. It still has to be removable, so this was my solution to make it a bit faster. This does increase your hands-on time, instead of just tossing it on the printer and then doing your thing. Just putting this in here in case you inspire anyone else to do this but they don't want to print the bottom.

I think there may even be cheaper sheets to use: https://www.amazon.com/gp/product/B00MR5EIN6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1