3-way switch AND sgl pole dimmer in one gang
It's not enough to get any dimmer. You need a dimmer that is compatible with your LED system.  That's a hard find, and diy.se is not a shop-for-me site.  We can help with how to navigate the limitations of the available tech. 

Very often these under-cabinet LED lights are 12 volts from a power supply.   If so, that is the place to do the dimming - after the power supply, on the 12 volt side, with a dimmer for that purpose.  Especially if you want to jazz it up with RGB LEDs or variable color temperature LEDs.  Have the switch just be a switch, and have a separate LED-optimized dimmer control under the cabinets where practical. 

That will make finding the right switch a lot easier.  All you need is a duplex 3-way switch.  A 3-way switch can substitute for a 2-way switch.  Just use the "common" and one other terminal, leave the other terminal unused.