The Wiki's
Amplifier models list and
Cabinet models list are my starting point. Look up amps you want to emulate in the first link, such as the Twin or Bandmaster, note the cabinet type or factory IR, then look it up in the second link for various flavors of the factory IRs.
Also, don't overlook the factory or Fractal Dyna-Cab packs because there are great sounding cabs that'll work with cleans.
Additionally, look at the factory presets as there are a number of amp+cab choices that work really well for cleans.
IMO, "clean" is tied mostly to the Amp block settings, especially how you're driving the amp, and the speaker/IR is coloring that sound a little. You can get great cleans from the "metal" amps by turning down the Amp block's settings. At that point pin the IR picker and start scrolling through them until you find what you're looking for.
As for specific "brands" of speakers, look into JBL and EV-12ML as they're known for extended range sound which will be captured by the IR. The (Robben) Ford preset for the Rumble amp with the EV-ish IRs or Dyna-Cabs are a great combination; See #38, "ODS-100", in the factory presets.