>>Where are rare fabrics obtained? Are they drops from enemies / in boxes or currently just from quests and the like?

Just quests/raffles/specific games/etc. AFAIK, only rare metals are available in the general game via RNG gods shining upon you.

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Uzmam! The Chairman will NOT be pleased to know you're trying to build outside of approved zones. I'd hate for you to be charged the taxes needed to have this place re-zoned. Head for the manor if you're feeling creative.