DRKV
Duke Fishron
Shop Expander

This mod solves the problem, by modifying tModLoader's shop setup process. It provides each mod with a new empty inventory to put items in, then combines the inventories. This new Expanded shop is then divided into pages for displaying.
Left clicking on the page selection arrows advances one page, right clicking will skip to the first/last page. The shop still functions as normal, but now you have a lot more space. As a bonus, you also get a full 28 slot empty page for the buyback buffer. This only shows up once you actually sell something by placing it into an empty slot in the shop, or shift clicking.
Whit this, the possibilities are quite literally endless. Shop Expander also comes with a simple API, to allow other mods to add as many shop items as they wish.

(Gfycat may have eaten a few frames there...
This is supposed to be every item from vanilla,
Thorium, Calamity, Spirit and imkSushi's Mod
resulting in over 200 pages.)
More technical information and downloads available on GitHub: https://github.com/DRKV333/ShopExpander
The mod is also available on the mod browser.
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