While I think it’s cool that you were 100% Glowforge here, You can buy square dowels for cheap in all manner of hardwoods at woodcraft.
Since you’re hiding them you can also buy plain old everyday dowels in various shapes from Home Depot too.
Iterating stuff takes time and materials, using dowels from a consistent source can speed your production a great deal.
Here’s an example of a thing made with Home Depot dowels as registration pins: