Your kid dropped the remote in the toilet, or it smashed to pieces after you dropped it on your marble floor one too many times. Or it just disappeared from plain sight. Sure, you could buy a programmable or universal remote, but they can be a hassle to set up, and it's hard to get used to a completely different button layout.
A replacement remote is just so much easier to use, but getting one from the original manufacturer can be a challenge in its own right. If you're stuck try New Remote Control, they stock original factory remotes for a vast array of products, but not everything. The site also sells used, refurbished and re-packaged factory remotes and generic remotes for TVs, VCRs, players, receivers, and all sorts of products. They also repair remotes. Replacement prices seem pretty reasonable, $14.95 for a Magnavox VCR or $27.95 for a Denon receiver remote, though I saw some remotes listed for over $100.
If you need a remote, why not see if New Remote Control has what you're looking for?
Or if you've used another source for replacement remotes, tell us about it in the Comments section.