Not readily available, but on eBay from time to time.
This towel was used as a makeshift cape for the Boba Fett Super Trooper during its initial review when it arrived in the US, in mid 1978.
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The towel is a thin beach-type towel, approx 31" x 55." It is 84% cotton/16% polyester. There are two versions of this towel, one with fringes on the short ends and one with no fringes. The one seen on the Super Trooper has fringes.