Is there anywhere that you can buy *custom* individual Lego-compatible bricks?
There are several ways to obtain pieces that are not in the LEGO pallette that I know of:

Through 3D printing at home. This has become much easier as 3D printers have seen significant improvements in resolution, precision and affordability. The challenge is to make a part that works as well as a regular LEGO brick, as that requires very tight tolerances. On the other hand, dimensions of common bricks are very easy to find in the public domain.

Via a 3D printing service using someone else’s design for a part. Check out Shapeways and even Etsy to see if a part has already been designed and manufactured by another fan. There used to be room on Bricklink for custom items like this, but since LEGO bought Bricklink these products have been removed from the site. Especially in the train hobby there are many individuals printing custom items such as wheels, track, connecting rods, couplers etc.

From a LEGO compatible brand. I would first look at reputable brands such as Mega Construx, Kre-o and the like, before going the illegal-clone route with companies like Lepin. The downside is that there are no part catalogs and trading sites for these brands (like Bricklink and Brickowl for LEGO), so you will need to look at sets and see if you can spot the piece you need. Perhaps some brands have a customer service line where you can ask questions about specific parts. Another downside is that color matching with your build can be problematic, but that likely holds for options 1&amp;2 as well.


Note that many AFOLs consider it part of the fun of building with LEGO to use only available parts to solve a particular challenge.