Where to look for a contractor for designing devices such as a specialized computer (motherboard)?

Question

Iron

Let's say you need to develop a device comparable in format and level of complexity to RaspberryPi (in fact, even, perhaps, simpler). RAM, chipset, CPU (ARM or even simpler), a couple of external interfaces. For very special needs (ready-made universal options like the same RaspberryPi are not suitable in principle).
Where to meddle with such tasks? Who in the world does this? Only manufacturers of motherboards like MSI, JetWay, etc. come to mind. and, in fact, the authors of RaspberryPi and analogues, but they are unlikely to condescend to small private orders.
I'm not suggesting anything to anyone yet, it's just interesting in principle, conceptually, "if suddenly."

Answer 1

This can theoretically be done by any board designer or team that exists in Russia. But when designing high-frequency multilayer boards with BGA chips, both the guides of chip manufacturers in general, as well as the experience of wiring (HW design) and testing specific similar specimens, are of great importance. Since you have ARM, there are enough organizations in Russia where such tasks were solved (for example, GPS receivers) and there is the necessary experience. As a result, your task is not too difficult, someone could do it under a freelance contract. What could not be said about Intel processors and standard motherboards.
The project includes at least 2 iterations of sample production, because Every design is subject to error.

Answer 2

You didn’t write what it is for you (it can launch into space or install it in a pacemaker), but something tells me that finding something mass-produced and suitable will be an order of magnitude cheaper than developing and ordering production.