Extended Reality (XR) Technologies enable the creation of immersive and interactive environments in which it is possible to safely test products and operational contexts at an early design stage. Such capability makes XR simulations extremely significant for the actual development of innovative modes of transport Urban Air Mobility (UAM). In fact, the implementation of transport of goods and passengers with autonomous and electrical vehicles in urban areas is still in its starting phase and, to efficiently progress, it requires testing, collaboration and visualization between different stakeholders with different needs and backgrounds. Moreover, XR can efficiently support the prediction of the social impact of UAM solutions. Since each UAM mission scenario involves visualizing one or more specific aircraft in a specific environment, there is a need to create a diverse library of 3D scenarios that are ready for simulation and can be tailored as required. These scenarios are based on 3D models of environments and aircraft that must meet complex functional and user requirements. This paper reports on a list of requirements for UAM 3D aircraft models for XR simulations, as well as the process for generating 3D UAM aircraft models to populate a database tailored for UAM XR-based simulations. The proposed four-phase process named identification, screening, tailoring and inclusion, is designed to simplify the modelling workflow, facilitating rapid model reuse and integration in XR environments.