I believe there are 90min SP miniDV tapes, but I have never seen local shops stock it. No, I am not refering to using the LP mode either.
But in the first place, why do you need such long running tapes? With some pre-planning and practice, you should be able to stop the recording, eject the used tape and insert a new one in a few seconds. Have your new tape ready in your pocket standing by(not in its protective cover), and once u come to a lull in the action, do the change.
So far, covered weddings with 60min tapes, and learnt never to use the LP mode(as far as possible). The video quality deteriorates rapidly, and the audio is effected.