Are you fine with having replicas? because you can make convincing props out of foam with paint.
If you want the real deal I suggest moving to a conservative state in the USA and opening a museum. More weapon restrictions are lifted from people who are displaying them to the public. In my state grenade launchers and flamethrowers are completely legal for citizens.
If you become a legitimate curator, the US Army might be willing to sell you land mines, grenades, mortars, torpedo, and possibly stinger missiles. However most of these will be disabled or made completely inert before being sold to you. but the grenades are mass produced and fairly cheap at 100 dollars each. expect to pay upwards of 50,000 dollars for a missile.
If you don't want to go legit I recommend you buy your explosives from an Irish / Russian dealer. Stay away from the Mexican cartel.
How you get the money I can't say. otherwise i would be rich myself