You can print out templates and cut them down to size with scissors or a
razor blade, in a pinch. It’s not particularly hard, and worst case, you
have to buy another $10 SIM card.
you can get the cutters/punches in chinatown. Just find a cell phone accessories store and ask for one. They’re a dime a dozen in Hong Kong, so you can usually get them at bargain prices.
Most stores charge $5 to cut the sim card for you, that gets expensive fast
when you have multiple phones in the family.
I ended up at International Village and bought a cutter for about $15
including taxes, took it back the next day as it was the wrong size, paid $25
total for a new cutter that does all 3 variations