Silicone rubber is used to make moulds because it is flexible and does not require a "mould release" to remove the acrylic casting from the mould. You can make acrylic duplicates out of any small object by making your own resin casting moulds. Silicone rubber moulding kits are sold in craft stores, which include instructions for mixing the silicone and hardener so that they harden correctly. Follow a specific procedure to create a mould that is ready for resin casting.
Measure and pour the silicone rubber from the kit into a plastic cup and add the amount of catalyst according to the directions that came with the kit. If the object that you are duplicating is only about 1 inch wide and 1/2 inch thick, you will need to add up to 3 cups so that it will make a mould large enough to hold it. Adjust the amount of silicone to the size of the object. Mix the two parts together with a plastic spoon.
Place the cup inside of a household vacuum chamber like the ones used for sealing food containers. Hook an electric vacuum pump up to the vacuum chamber and run it for three to five minutes to degas the rubber silicone mixture. The silicone is free of gas once it is done bubbling.
Set the object you are duplicating in the bottom of a disposable aluminium baking pan that is about twice the width of the object and twice the thickness; the kind of pans used to bake individual small pastries are ideal. Pour the degassed silicone mixture slowly into the pan so that is surrounds the object and covers it about 1/2 inch. Let the silicone mould harden for 20 hours.
Cut a slit on four sides of the top edge of the aluminium pan with a knife and gently tear it and peel it away from the rubber mould. Once the mould is free from the aluminium pan, turn it over and gently squeeze it to pop the object out.