Replacement bulbs

Hi,

I am trying to find the outside amber bulb for my 05 Colorado. The bulb number is 3757KA (not nak or ak, those bulbs don't work, they don't even have the same number of filament connections). The bulb acts as a turn signal, a DRL/Parking light and is supposed to activate when the headlights are manually activated. The NAK / AK versions don't allow all the functions, ie. when the headlights or parking lights are activated, the buld doesn't come on. The AC Delco replacement is the 3757 NAK. Can anyone point me in the right direction?