I dont need to, I'm an owned of one of those macs and mine has Firewire. I've never had the need to use Thunderbolt... and thats largely in part of the fact that my macbook has more thunderbolt ports than I have ever seen thunderbolt devices on store shelves: ZERO.
The Apple Store, online as well as brick-and-mortar, have plenty of Thunderbolt drives from several manufacturers.
So does Amazon, Best Buy, B&H, and many others. Sure, perhaps in your town there may not be any on the store shelves. But since you post here, you have Internet access, and a quick online search for Thunderbolt products will lead to many potential shopping hits.
There are many many products that never will show up on my local retailer's shelf. That doesn't mean there are no products available, nor are there no customers for those products. Many products sell very well and never appear on the retailers shelf at all.
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Looks like it has an SSD option, but that's only up to 256... Meh... Double meh.
El Gato now has a 512GB SSD with Thunderbolt and USB3.0 ports.
Only $899.95 USD
http://www.elgato.com/storage/thunderbolt-drive-512gb