There should be a label on the back of the TV with the model number and brand.
The TVs also all support IR remotes, so you can pick up a universal IR remote locally for little money. Just make sure they list Roku as a supported device.
Make sure it lists Roku tv's! A remote with roku listed doesn't mean it will control a roku tv. Go to walmart and get the One-For-All urc-7935, on sale at $16.88. Or get it used on Ebay for abour $10.