sample find

You're going to have to write a program that has something like the following in it:
rednet.open("right")
local id, message = rednet.receive() --Wait for a message to be sent to the turtle so you have time to set up the gps servers and such
local x,y,z = gps.locate()
rednet.send(id, "I am at: "..x..","..y..","..z)

For the computer, have a program that does this:
rednet.open("top")--Or whatever side your computer has the modem on
rednet.broadcast(" ")
local id, message = rednet.receive()
print(message)