Try Cromwell Tools, they have some stuff called 01 tool steel, it's very reasonably pricedLooking for 2 pieces 650 x 55 x 6mm tool steel
No shorter than the 650 mm but other 2 measurements could be bigger
Cash awaits
Looking for 2 pieces 650 x 55 x 6mm tool steel
Thinking about it a planer thicknesser blade would do it.