you can buy it anywhere, any airline, or even sites like expedia, the think is that you need to pay more - way more - for refundable tickets.
Any ticket can be cancelled, but most can't be refunded.
I recommend going to Southwest.com. They fly between PHL and TPA, they have the most nonstops, and they have the lowest priced FULLY refundable fare in every one of the cases I have needed that.
Plus if you get a discounted, nonrefundable fare and don't need to go to game 6, then you have 1 year to reuse the full amount of your ticket and don't have to pay any re-ticketing fees or any of that nonsense that the legacy guys will hit you with.
Ditto to what Marymiss said. It's very simple to buy an unrestricted ticket, and you can purchase one just about anywhere; the only problem is the hefty price tag that comes with it.
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