Why aren't the variables P28 IND80 and P26 IND10 available for the 1910 census?

I’m looking for information in industry structure. I want to compare different industry classification schemes, and I understood that the 1910 census was the first to ask questions about specific industry. I would like to compare this variable, which I understand is stored in the P26 IND10 variable, with the information backed out from the occupation, stored in the IND1950 variable. However IND10 is not available as a variable when I search for it in the “create an extract” page. My information about the IND10 variable comes from this page.

The 1910 sample in IPUMS-USA is actually a combination of several samples. The specific sample each record stems from can be seen by viewing the SAMP1910 variable and the 1910 sample design page. The original 1910 PUMS sample is not available through IPUMS, but can be found on the ICPSR website here. This data file should have the variables you are looking for.