Replacement iMac G3 Chasis?
I know of no vendor that sells the slot loading inner bezel for your imac whether it’s OEM or aftermarket.

You could purchase a machine from ebay (or similar) and hope they pack it properly so as not to destroy the inner bezel in shipping, or you can try and gorrilla glue the original bezel together so you can scan and 3-d print a new one or hire someone to fabricate a replacement.