I recently received an email from an Australian parent unable to find the crinkle cutter locally. No matter where you live, these are not easy to find. Look in little independent kitchen stores. It can help if you are able to choose one in person rather than online. Although you may find one type popular online, in person I've seen families use a whole range of different crinkle cutters, there is no one brand that is endorsed or labelled as Montessori. 

I first used a crinkle cutter with Caspar back in 2011. I received it as part of a pack of practical life materials from Montessori Child. The pack came with little laminated instruction cards and materials for each activity. It was perfect for a first-time parent. Otto has been using a round tipped serrated knife to cut soft things like banana and egg from around 13-14 months. But we will soon introduce the crinkle cutter as a way to cut harder things like root vegetables. The advantage of the crinkle cutter and perhaps why they are so popular is they allow the child to cut with two hands on the cutter, once they learn how to do it, it's quite simple. 

Here are a few sources of crinkle cutters:

Australia

Crinkle Vegetable Slicer at I Am Montessori. "Loved in our classes so much! "

D.Line Crinkle Vegetable Cutter at Kitchen Discounts.

D.Line Crinkle Vegetable Cutter at House. 

D.Line Crinkle Vegetable Cutter at Robins Kitchen. 

Avanti Crinkle Vegetable Cutter at Kitchen Warehouse.

Appetito Crinkle Vegetable Cutter  at Victoria's Basement. 

MSC Wavy Knife at Kitchen Discounts - I have purchased these many times and they are the Joie crinkle cutters. 

Large Serrated Cutter at The Kid Specialist. We have not tried this one, but I wouldn't hesitate to contact Ruth first if you have any questions.

Look in physical kitchen stores, our old local kitchen supply store (at the Belconnen markets) used to stock the Joie wavy knife and lots of other favourite child-sized kitchen items. Other good early/first knives to use in Australia include the Foost First Knife, and Kiddi Kutter. In Australia, there are heaps of options!!

USA

Joie Fruit and Vegetable Wavy Chopper Knife at Amazon.

MSC International Stainless Steel Crinkle Cutter at Amazon.

Wavy Chopper Crinkle-Cut Knife at Montessori Services.

Fox Run Vegetable/Cheese Slicer at Amazon.

UK

Crinkle Cutter (wavy knife) at Manine Montessori. 

Crinkle Cutter  at Absorbent Minds Montessori.

Tala Stainless Steel Crinkle Chip Cutter at Amazon. This is the one I've found most popular with UK families.

Faringdon Stainless Steel Crinkle Cutter at Amazon.

Crinkle Cutter at Dunelm.

Canada

Atelier Saint-cerf - this is on Etsy and they ship international. We have this one and I was sceptical about using a wooden knife. But it works, just as well as all of our crinkle cutters. This one has the advantage that it is completely compostable and the blade is flat. Although it can't go into the dishwasher. 

There are a lot of other types of crinkle cutters available, what is important is that the knife works for you and your child. You can see how Otis uses both the black handle and the Joie crinkle cutters at 17 months here.