i've never seen a place or service to get lids.
i think your options are:
- get a new pot
- ask an artist
- acquire tools and skills to make a ceramic lid
- settle for making a simple lid with a focus on basic functionality
for the last option, perhaps you could fashion a very basic lid out of sheet metal. casting a lid out of various materials also would not be outside the realm of possibility. you could look into investment casting, for example. perhaps even starting with CAD and FDM to make a mold to yield your wax pattern.
realistically, i'd just get a new pot or hope to eventually find a well fitting lid from a random pot you don't care about.
this is a long shot, but i guess you could also put out a WTB for a lid with suitable dimensions. perhaps people could look at their collections of pots they don't care about, and a donor lid could be found.