The operating airline (AA or UA) must make award seats available to partner programs. Typically, they only make the lowest "saver" tier available to partners, and typically they make the same seats available to all partners. If you look at aa.com and united.com and do not see low mileage award seats available, you will not find them on any partner. This is more difficult to judge than it used to be, because airlines have replaced fixed tiers with dynamic award pricing. I would not expect much availability if flying to Florida in the winter.

When you look at Amex Travel you are not seeing award seats, you are purchasing a ticket with money, and then using points to offset the charge.