Add a flag to each record, say called selected.
Open a recordset of all data where selected is false.
Get a random number based on the number of records in the recordset. e.g.
Int((MyRecordset.Recordcount - 1) * Rnd + 1)
Move through the recordset that many times, get the data and set the new flag 'selected' to true
Repeat the process until the record count is 0.