I am not aware of any that are inset in worktops, they would probably get too hot and full of food gunk, so unsanitary, and fibreoptics or LEDS would have to be protected at least by a plastic or perspex (which can be scratched and look terrible). But have you researched what they do in cocktail bars with lights (fibreoptic or otherwise) set underneath a coloured or frosted glass worktop sometimes covered again by clear glass, or a regular worktop set on top of a box of glass so the light come out from below ? It might still get scratched if you don’t use chopping boards, but with care it would work - I have a glass topped table and it still looks as good as new.

Yes, you should go on the net and look under Dot Lighting and look for LED lights. You can get ones in different sizes and shapes, but you should look at the IP rating which should not be less than IP68. The more expensive alternative is from