Have a look on ebay for Disney Laserdiscs, a lot you'll be able to get buyitnow in ebay stores for a few dollars. looking now you can get the regular version of The Lion King for $3 and the CAV boxset for $10, postage puts them up - but if you look around you might find someone selling all the ones you want and you can save on postage.
Is there a Laserdisc of Mary Poppins with the correct aspect ration? Has this not come out on DVD yet..?