One of my university teachers had an older model, I think. He had more than 5 keys missing. He would literally carry a full fledged desktop keyboard (that was twice the size of that mac) and just place on top of the notebook when working 
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Generally speaking, especially if you are in US/Canada, you can easily source a replacement and replace it yourself, there are a lot of options out there and the price will be good too. As for labor it is annoying as you will have to literally take out metal rivets, however it is a job that even a beginner can do.
