Many years ago, when the IMSA convention was in Milwaukee, I got a trip through their signal shops. We were all super-impressed with the things they were doing! They built many of their own parts, having them cast locally. They refurbished everything possible rather than throwing it away.
It was explained to us that Milwaukee has many foundries and machine shops available to contract this type of work. The second factor is that the area's tough winter keeps the signal crew out of the field except for necessary maintenance. Thus they have extra shop time available in the winter to create their own parts and to refurbish equipment.