My guess is that you will not find a source of new bases.
There may be some lying around in a dusty corner of a factory in a distant land but there's no profit to be made holding stock on the off-chance that someone might wish to buy one one day. Better by far to sell them a new chair complete with base.
Better Homes & Gardens will have bought the chairs either from a distributor or direct from the manufacturer - it is here you should be looking if you're to succeed.
Good luck...
Peccavi, July 2013