This module can be found on Github and Terraform Registry

This module creates an AWS Route Table for Transit Gateway, and its associations and propagations.
It is designed to be used in collaboration with the official TGW module by AWS [Github, TF Registry].
While the official TGW module does include some route table functionality, the advantage of this module is better support for cross-account attachments and easier implementation of multiple route tables for the same TGW, thus being able to implement multiple routing domains (More details here).