I had planned to spend more time on this but I'm impatient so here it is. The concept isn't selling the blocks but the molds to create the blocks. Inspiration came while I was running and noticed that a neighbor made an entire wall from cement using an old coffee tin as the mold. Turns out cement dye is pretty common which helps bring the original Tertis theme to life. This could be a DIY project but the margin of a few stamped sheet aluminum molds would make it profitable in the right venue.
Why an arcade in the garden???
No, I don't see grandma going out to purchase a Squared Flower Bed kit or anything in the Garden Arcade series. However, I am aware of a growing trend of urban gardening; even some friends from college, who have the capability, have some sort of garden or flower bed. The arcade kids of the 70's -80's have homes. The tools to create the garden exist. Creating an nostalgic element or novel contrast to spice up a generally stereotypical garden environment should be a breath of fresh air to some users.