>>7119271The easiest answer would be Games Workshop, that or eBay. If you're unfamiliar with Warhammer model stuff, just know that it's less Gunpla and more Revell in terms of build and contruction. If you really want to go crazy with a Contemptor you could go to Forgeworld, find some magnets, and do this...
https://www.youtube.com/watch?v=wfJiuWnl0T8...although that is more moderate to advanced level work there and to be quite frank Forgeworld resin is generally frustrating to work with..