Specialty manga stores or comic bookshops could be a good place to start. Sometimes they have rare or specific box sets like the one you're looking for. You can also check their websites if they have an online presence. Additionally, some conventions or comic expos might have vendors selling such items.
The cost might be high because Mushishi has a dedicated fan base and is considered a collector's item. Also, the production process, including the quality of the paper and illustrations, could contribute to the expense.
If not under warranty, you could try to fix it yourself if the damage is minor. Maybe some glue or tape could do the trick. But for major damages, it might be best to look for a professional repair service or consider buying a new one.
The shelf for the set-top box could be placed according to personal preference and actual situation. Common placement suggestions included the TV cabinet, the wall, and the top of the TV. Placing a set-top box on the TV cabinet could make it easy to plug and unplug the cable without affecting the beauty of the TV. In addition, you can also choose to hang the set-top box shelf on the wall, which saves space and is more beautiful. On e-commerce platforms such as Taobao, Lynx, and Jingdong, you can find shelves for set-top boxes of various brands and prices.