Yes. If the A3000 uses a DIN-style connector, you can use a standard PC AT to PS/2 keyboard adaptor you can get from a good computer store.
Even though PC and Amiga keyboards are completely incompatible, the adaptors that convert big DIN PC keyboards to little PS/2 ones are also suitable for converting A2000 DIN-style Amiga keyboards to A4000 PS/2 style ones.
