You'll need to either find a universal remote from a local store -- Target, Walmart, Family Dollar, Best Buy, etc -- that supports Roku TV (not just Roku, but explicitly says Roku TV, as the codes are different), or you'll need to find a Roku Voice Remote ($20) from a store or online. https://www.roku.com/products/accessories/roku-tv
While the Voice Remote is a little more expensive, it does eliminate the need for direct line of sight. It's not an IR remote like the remote that came with the Roku TV.
DBDukes http://www.dbdukes.com/Roku Ultra (4660) Roku Streambar (9102) Roku Streaming Stick+ (3810)