We need a travelling long distance microscope for measurement of crack length

Hi

I am looking for a travelling long distance microscope for measurement of crack length. I will use this microscope on Instron fatigue test machine. I found some long distance microscopes on the web. But they are not appropriate for us. I attached a figure showing the travelling microscope that I would like to buy.

Do you have any suggestion about it? Where can I find it?

Thanks