How to add a jumper in Orcad Capture

you can get PSPICE model from manufacturer company, search on google for example "LM239 PSPICE Model" this will lead you to texas instrument site datasheet page. scroll down and you will see they have provided with PSPICE model.

I've found a guide in the TI's website.

I am trying to add Diac component into my OrCAD v16.5 Schematic Layout.

The subcircuit you listed is for doing simulations BUT you only want it to be a component in the schematic. Yes?

Find a component that looks like a diac (maybe an SCR or a diode) and place it somewhere on your schematic page. Right click the component and selct "edit part". This takes you to a new screen where you can edit the circuit symbol to be whatever shape you want - you can add pins, rename pins and totally redraw it to how you want it to look.

When done editing the part leave edit mode by pressing the X in the top right hand corner (as you would when closing down a sheet of a schematic).

OrCAD will then ask you if you want to update all parts - just select the option that says something like "only update this part" and hey presto you've edited a component and in your schematic it should look like a diac (or whatever you redrew).