I need to create some iron plates and bands to go onto my giant trebuchet for the "Incoming!" campaign... Was wondering what you all might suggest... Was thinking lead foil, or a similar item... Anyone else have any great ideas? Also, will need 1/35th scale rope, from the medieval period... Was thinking I might unravel some jute twine, but would appreciate any ideas or suggestions...

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One cheap alternative for bands etc. is aluminium foil trays. The type you get in the take-aways. these can be bought as storage containers as well in most big supermarkets. Good memory, take glue and paint well.
Good hardware stores have thin sheets of brass. Ask for shimming sheets or material for shimming. We get them all the time at work when we need to ensure parallelity between pressure plates.
Good rope can be bought in hobby shops, especially thos that deal in railroads and ships.