RUSAN of Croatia now make an incredible 2.5x Monocular to attach to most thermal imaging devices. The 2.5x Magnification Ocular comes with an adapter to use with Rusan's Modular Connectors - available in various sizes.
Other than the 2.5x Magnification Ocular with Adapter, you would need to correct Modular Connector with the corresponding thread size for your thermal imaging unit. See link here for appropriate connectors: https://www.shootingwarehouse.com/products/rusan-modular-adapter-connector?variant=40090620297350
We can special order ANY adapter that we don't have IN STOCK - turnaround time is typically around 3-4 weeks.
Here's a VIDEO on how the unit attaches to a Leica Calonox Sight Thermal Imaging Unit