Currently there is no renewable way of getting redstone (unless its trading with villagers), my suggestion is witch spawners, theres already most mob spawners that is usually unobtainable (creeper, zombie pigmen, enderman etc) a witch spawner would be a good implementation, redstone does not sell for a lot nor does any of the other drops from the witch spawner and a natural witch grinder would be near impossible due to spawn rates of mobs, not to mention the claims required. It would not only drop redstone which is useful, the full list of its drops are redstone, glowstone, sugar, gunpowder, glass bottles, spider eyes, and sticks. None of these are afkably obtainable except gunpowder and sugar. (spider eyes only drop when spiders are killed by a player)
Support It's a useful spawner unlike most others and would be a good replacement to the Slime spawner that Kinsey removed for being trash. Maybe replace the Slime spawner with a witch one completely (both /shop and crate rewards wise)?