Question :

Where can I download the drivers for the IR189USB or OC4USB cable?

Answer:  

There are two revisions of cable in existence, the first revision has no label on the infra-red part of the cable and the 2nd revision has a label REV II on the Infra-red part of the cable.
The old revisions cable are no longer supported and need to be replaced!  A new cable can be ordered from a local Fluke distributor

IR189USB REV II :

OC4USB REV II :

For the cables with a REV II  label, Fluke uses the same drivers for the IR189USB and OC4USB cables and are using FTDI drivers. These drivers a available on the website of FTDI.

Link to FTDI website : https://ftdichip.com/drivers/vcp-drivers/

Download the executable file for easy installation or one of the zip-files ( 32-bit / 64-bit) for manual installation.  The installation guides are also available on the same page