Shelves can be tricky to find. That one I had came from Ranchhouse cages on ebay. They do solid wood shelves that come with all the fittings for bars so very easy to attach. In various different sizes. Since the pandemic they don't have as many options but will usually make you one to a specific size if you ask. I just bought one that was 25 cm deep I think and 20" wide - which was a bit too wide so we had to cut a bit off to fit the inside of the cage. You also need to cut a small corner off at each side as the inside corners of the cage are actually curved. I can't remember where I got the ladder.
Or you can get something like Luna has - two of these overlapping.
https://www.amazon.co.uk/Trixie-Natu...00LJV4578&th=1