It looks like LM319 is a National Semiconductor (or Fairchirld) part. We do work with National Semiconductor (now acquired by Texas Instruments) to get their SPICE models directly into Multisim as simulatable parts.
However in this case, Nat Semi doesn't provide a simulation model for the LM319. You can find the product page here. On Nat Semi's website, you can look for models by clicking on the "Tools" menu at the left.
Your best bet would be to contact them directly and request a model. Given a SPICE model, you can create a component using this guide.
In general, when a part-specific model is not available, you can use a more generic simulation model like the "COMPARATOR_VIRTUAL". This allows you to look at a data sheet and specify certain characteristics like slew rate and gain to get an understanding of how this component will behave within your circuit.
Mark J.
National Instruments
