Unfortunately the C15 Chassis is indeed end of life and the motherboards are no longer (and haven’t been for some time) being produced by the manufacturer. Even second hand/reconditioned boards are becoming very hard to find, especially the B4 variant a graphics chip and TPM such as yours. Due to the nature of laptops the motherboard is designed to specifically fit a chassis so installing another board in the unit would not be a viable option. However there are 4 versions of the board that will fit your machine :
C15B1 - No TPM or GFX chip
C15B2 - No TPM but has a GFX chip
C15B3 - TPM but NO GFX chip
C15B4 - TPM and GFX chip
They would all work in your machine but depending on what you are planning to use the machine for should you be able to repair it, there would be some trade offs.
I can understand your frustration with being left with a unit that no longer functions, the only realistic option would be to search the web in the hope that someone may have one for sale, however a motherboard replacement on a laptop is not something that we would suggest consumers undertake as this does involve complete disassembly of the laptop, this should only be undertaken by someone familiar with laptop repairs as it can be very easy to damage either the chassis or the internal components during this process and would be entirely under your own risk.
I know this is not necessarily the news you were hoping for but if there is anything else I might be able to help you with or you require any clarification on the above please feel free to contact me