Past users have solved this frustrating problem. You can find their solutions with a Google search like "InDesign data merge multiple sequential items on one page" without quotes.
Frankie at Quad wrote:
I need to number tickets, 8 up on a tabloid page, in InDesign (CS5)
I have found out how to use data merge, but it won't allow me to select more than one data source at a time, therefore, making me use 800 sheets of paper instead of 100. That's not acceptable!! Is there a way to merge the pdfs if I make 8 different ones in the places they need to be? Each file that I export will have 100 pages, so is there a way to merge the files to put all eight tickets on each sheet, sequentially? This is driving me nuts!!!!!!!
Data merge is perfectly capable of doing 8-up numbering. It's all in how you set up your data set and the merge.
You can either put 8 numbers in one record (8 columns) and do a single record per page into a merge template with placeholders for the 8 fields, or you can do a single number per record (1 column) and do a multiple records per page merge. The latter is accomplished by building only one instance of the ticket layout in the upper left position on the merge template. ID will duplicate all of this as many times as will fit onthe page according to the margin and spacing parameters you set inthe multiple records merge options.
This is all explained pretty well in the Help files...