I had it done at a local AC-Delco repair depot- "Eastern Electronics" located in Hackensack NJ. They are the ones that repair all the core radios, alternators, electronic modules, etc... for the region. I gave them the speedo & faceplate and told them what car it was for. They assembled it and calibrated it in 1 day.
That may not help you much up north so just go to the local GM dealer and ask them where they send broken electronics to be fixed...