Labo launches today in North America, and it's heartening to know that once kits are in the hands of players all over the nation (Europe has to wait until next week, sadly), we don't need to worry about broken parts - because Nintendo has kindly put a load of replacement items on its North American web store.
With prices ranging from $1.99 for a sheet of reflective stickers to $11.99 for packs of cardboard for the kits, Nintendo has pretty much everything covered here.
If you'd like to try making these yourself, Nintendo has also published PDFs of all the various bits so you can cut out your own parts.
Given the nature of the material involved it's almost inevitable that you're going to need some spare elements at some point during your time with Labo, so we're glad Nintendo has made sourcing replacements so easy - and relatively cheap, too.
Thanks to Ernest_The_Crab for the tip!