And approximate orbital State Vector value can be computed from orbital elements.
This is an easy way to drive a ‘plausible’ orbit for something for which no ephemeris or TLE data is available.
Solar System Dynamics maintains a database of over 1 million small bodies (asteroids, comets, etc) including orbital elements. This data can be downloaded in .csv format, and then easily read into Unreal Engine.
Ephemeris data for a Small Body like Comet Hyakutake can also be generated on-demand from the Horizons system.
Ephemeris data is always preferable when you have it.