I don't see anyone in this thread talk about a virtual instrument. The Keithley 181 pre-dates the release of the first version of LabVIEW by a couple of years, so it's not surprising that there are no LabVIEW drivers available. However, these drivers are only fairly thin wrappers around VISA, so invoking VISA directly is not all that complicated. A bit more complicated if you want to wait for SRQ, but I'm sure you can find examples of how to wait for SRQ and then perform a VISA read in LabVIEW.
If you are familiar with LabVIEW development, then reading the values using
VISA Read and parsing the results should be fairly straight-forward.