Reddit mentions of Island Presents: Ska / Various

"Simmer Down" is ska from about '64. There are a bunch of 60's ska CDs out there but be careful because many, especially the compilations, have overlapping tracks. Here are some examples:

• Island Records Presents Ska
  
• Treasure Isle Records Presents Ska
  
• Prince Buster - Fabulous Greatest Hits
  
• Bob Marley & Wailers - One Love at Studio One
  
  "Harder They Come" is early reggae from about '72. Between ska and reggae was a style called rock steady that was sort of like slow ska. Most ska CDs will have at least a few rock steady songs mixed in too. It's a little later than the time period of "Harder They Come" but the best selling reggae record of all time is Bob Marley - Legend and it's worth checking out if you're not familiar with it. Here are some examples of early reggae:
  
  
• Original Labour of Love Collection
  
• Harder They Come OST
  
• Jimmy Cliff - Jimmy Cliff
  
• Desmond Dekker - 007, Best of...
  
• Toots & Maytals - Pressure Drop