If the code is not written on the radio casing or inside the glove compartment, in/under the ashtray, behind the sun visor (or similar "hidden" place inside your car ) then the majority of HONDA codes may be available here
https://radio-navicode.honda.com
You will require the car VIN number and Radio serial Number
If they cannot provide your code then you will have to try your HONDA Main Dealer .....or a Decode Service who will plug in a laptop to read/recode the memory chip (EEPROM)