I think I found the exact original prop of the Hoth Trench Trooper belt buckle.
It is called a "Ministry of Defense plate" or MOD plate and looks to be the perfect size, has the curved side edges, and the belt loops. It makes sense that it is regular issue British surplus.
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Belt Buckle Metal Plain Chrome Width 67mm Height 56mm, suitable for belt width up to 57mm With runner Be sure to add me to your favourites list !
uniformstorelondon.com
Standard issue UK MoD (Ministry of Defence) plate and catch. Available in brass or chrome. Size: 90 mm (L) x 60 mm (W).
www.cadetdirect.com
British Forces type rectangular belt plate with catch in two metal finishes.
www.survivalaids.com
This silver plain buckle is worn on a belt by members of the British Army. Dimensions: 7.5cm x 6cmMain Composition: Brass / Silver PlatedNSN: 8455-99-514-4478Force: British Army
www.wyedeanstores.com