Can you explain to us why you just didn't go with the AT28C0x0 EEProm series?
The 'AT28C010' has plenty of stock, though, you would need to piggyback 2 of them with a logic gate for swapping the enable on the upper address.
The 020 and 040 are too hard to get and at over 100$ each, I would stick with the cheap eproms.
It would be cheaper to use a serial prom to fill a static ram at power-up and simulate your parallel pages flash ram.