Well..
I rapidly needed one for my current brew..I used a two piece handy airlock from wilko, removed the lid, got my only spare bit of tube which was part of a basic syphon kit, and pulled it off the syphon cane. The tube wouldn't fit over the internal tube of the airlock even by heating in boiling water so I cut a short spigot off the syphon cane to join them..an empty pop bottle with some starSan solution completes it. The s type airlock is woefully inadequate for vigorous fermentation. ..you also need something to stand your fv in like a tray or trug as the lid can burst off!
Cheers
Clint