Gotta ask: just how many are you looking to buy? You said "a gift" which is really easy under most normal circumstances. Best Buy. Walmart. Target. Amazon. Roku direct.
If you're looking to buy enough to be a reseller, there's a Reseller Form link available from the Roku "Contact Us" page. https://www.roku.com/about/contact
If you're just looking to buy a device, your best bet is to go with the online store purchase route from a retailer mentioned. If you have questions prior to purchase, you're already in the right place for that. Just ask.
DBDukes
http://www.dbdukes.com/
Roku Ultra (4660)
Roku Streambar (9102)
Roku Streaming Stick+ (3810)
