I would guess a bank or a currency exchange, but they're likely to give you only bills. You could also ask at Duty Free shops. You don't need that many so you could probably just exchange 2 Euros worth for 30 nickels and 50 pennies.
I was checking the quantities for my Carson City metal coins as a fill-in for GWT cardboard coins last night and they came up short unfortunately. I did have enough of my Drawlab metal coins in their Wild West series to use in GWT. They are heftier in weight, have a nominal size difference between the values, come in 3 different colors, but lack a number on either face so you mentally assign then as preferred.
The best part of thr Drawlab coins is how they sound when they clank together. Seeing them stacked up or layered in a row is much more appealling than current nickels and pennies. Of course I've seen those for dozens of years so they aren't overly special to me.
Have fun with whatever coins you find- it's a component that should feel more thematic once replaced.