Can someone help me understand DIACs and TRIACs
There are many diacs (I don't believe it should be capitalized) available on the market, most currently sold are variations on the DB3 part number. 

Older numbers included the ST2 originated by General Electric. 

A diac is a bidirectional switch that breaks over at a controlled voltage in each direction. It does not behave like two zener diodes- it has a negative resistance characteristic like a thyristor- the voltage across it drops (assuming the current is limited) and it will continue to conduct until the current drops below the holding current. 

A similar functionality is provided by a SIDAC device.

You could replace a diac with four BJTs (2 NPN/2 PNP) and a couple zeners and a couple resistors, but a couple ordinary diodes are not going to behave the same.