"Readily available" simply means these type switches are commonly used, so you should be able to find a replacement somewhere. You'll have to hunt at electronic stores. I measure the switch at 4.56mm. Now these switches don't come in these exact sizes, so this may either be a 4.5 or 5mm switch... and I don't know which it would be.
If you're going to fix this yourself, then you should pull the board out of the Vamo (see
THIS), and take it to a electronics store to match the switch. Or call around to places like Digikey, Radio Shack, or a local electronics shop and ask them questions.
This is what the Vamo board looks like, and you can see what the small square tactile switch looks like.
View attachment 200963
The other option is to buy an entire replacement board for about $21 + shipping (see
THIS), or buy a new Vamo, save the old one for repair one day, or for parts. Personally, I would buy a new Vamo, then try to get the broken one repaired... but that's just me... in fact, that's the reason I can show you this photo.