You could do something like this, which queries all tapes with data written to them in the past few days.

mminfo -av -q "sscreate > 1/4/2008" -r "ssid, sscreate, volume, volid, barcode"
or
mminfo -av -t "7 days ago" -r "ssid, sscreate, volume, volid, barcode"

Note that the same tape might be returned twice, so you might want to do:
mminfo -av -t "7 days ago" -r "volume" | sort | uniq

Thanks a lot. All worked ok.