Whole Number (integer) fields in an InfoPath form published as site columns do not show up in the Site Column Gallery. I found a few others who ran into same issue (one in fact had his site column disappear from the Gallery after changing it from text to integer). What gives? Is integer reserved by the system and therefore site columns of integer type get "hidden"?
I was able to "find" and delete the columns using the 'http://yourserver/yoursite/_layouts/fldedit.aspx?field=' URL (you type in the name of the column after the = )
Tip: You can determine the URL of the site column by extrapolating information from the URL of a site column URL you can see. I found this tip on the Internet somewhere after almost pulling my hair out trying to find the "missing" columns (sorry, can't recall where). For example, I needed to delete the Category and SubCategory columns. I saw that the URL for the File Description column, which is a text field and visible in the Gallery, was '_layouts/fldedit.aspx?field=File%5Fx0020%5FSub%5Fx0020%5FFileDescription&Source=%2Fsites%2Fit%2F%5Flayouts%2Fmngfield%2Easpx%3FFilter%3DAll%2520Groups'. I simply replaced FileDescription with Category and voila, the Category site column page opened and I was able to delete that column. SubCategory was a bit tougher to figure out because SharePoint had created the column name as two words: Sub Category. But once I placed %5Fx0020%5F (the padding) between the words the URL worked and I was also able to delete that column. I was then able to change the fields to text and republish recreating the site columns from scratch.