Both a tribute to ubiquitous, and lovely, hexagonal colour pencils, and a representation of what was coined by Joris Peels as 'combinatory manufacturing'.
Combine the connector piece with any set of 36 standard hexagonal pencils of about 7.0 mm cross section (measured at the smallest diameter). These types of sets are available around the world from many department stores and art supply stores - I’ve seen good sets for as little as 5 euro.
Examples of pencils that fit are Stabilo Aquacolor 1600, and Caran d’Ache Prismalo I, but there are many more. I’ve recently heard that in the US, Prismacolor Verithin Colored Pencils (available from Amazon and others) work well. Normal black pencils often have the same size and shape and can be used too. Assembly may leave slight marks on pencils.