The more technical term for a walkie-talkie is handheld transceiver. Amateur radio publications are likely sources for transceivers. Some have been adapted to portable use. Something that performs well will likely be very challenging for all but the most experienced - though it can be done.
Could you be any more vague with your request?
Before we could even attempt to assist you with a project that you should be able to locate on the Internet with some ease, we'd need to know what your specifications for the unit are. What frequency band, single or multiple channels, power output, etc. Of course it also matters a great deal as to what country you are using it in so as to comply with their regulations on transmitting equipment. Sheesh!
I told him on another forum that Google has links to 254,000 circuits for walkie talkies for him to select from. Most are cheap kids toys. Some even use vacuum tubes!