I was thinking of the TL431B 2.495V reference diode. I'm sure there are others as well.
The zener probes reference is a LT1004 2.5 reference on the actuall circuit sorry for not mension it. The schematic was made in spice orcad, this part was not aviable to simulate so I used something alternative.The second zener (the amp reference) its actually a zener diode.