Other than serial (IIC, SPI etc) the one and only reliable way to add I/O is Memory Mapped I/O (MMIO). With MMIO you decode a block of addresses and direct the write and read to latches and gates (easily accomplished in a CPLD). WSD (now part of ST micro) has a series of psd chips which combine RAM and MMIO.

However, in your case, it would be far simpler to get hold of a chip such as the P89C668 with enough internal RAM and flash to leave all ports free for I/O.

Erik