Hello!
Answering this question: yes, it is possible to obtain an infinite amount of these items, but there are some rules when obtaining them.
Rule number 1: there is a 1 hour cooldown to get more Dragon Egg Shells.
Rule number 2: it can only be obtained if your character is on sub-mission 1 or 2 of The Great Hunger mission from Krailos Quest (link here).
To not lock your main character you can create a maker to collect decoration items, I highly recommend that you do this, there are a lot of items that can be obtained this way.
Source: Tests made by me and fed into the official fansite TibiaLight, this link. It is in Portuguese at the moment and there are a lot of items tested.
I hope this answer can be useful.