Bikepunx.com are making loads of nice steel bits in the UK, including BIG sprockets, shimano micro-spline compatible singlespeed sprockets and stainless chainring for most cranksets BCDS.
Their bits are really nice. ( 43T GRX BCD chainring in 3/32, on Sanded Grx Cranks)
here seems as good a place as any for this: anyone know who makes a big singlespeed cog? looking for 23 or 24t ideally.