Is there a website where you can buy a prepaid Visa gift card?

It depends on where you're located and what your preferences are in terms of merchant.

You can also buy Visa PrePaid cards from itunes-giftcards.com/iTunes_match.html They have all denominators and they send the information all to your email.

GiftCards.com sells Visa gift card online. You can also buy online at Walmart.com or target.com.