Go back to the project you were viewing. Scroll down to the end of the project and there is a section to ask questions. This is the general forum, and the author may never see, nor know you are looking for info on their post.
Hi Laura. I found the bicycle mailbox that you are talking about. It does not give info on the mold. I went on line after that and found molds just like the one mentioned. You can buy them at Lowe's. They have many to choose from.
If the link below is the project you saw, you should be able to find the pavers at a big box home store. I saw the same thing in Lowes this summer. I don't know if they still have them or if they sold out, but the seem to be a popular paver look this year. Wishing you the best.