Any after market radio GURU's here?

I am having an issue with installing a after market radio (Dual XDM270) in a friends 2003 Mazda Protege 5. The radio is set in the dash and wired up and everything works except the AM/FM receiver, the factory antenna will not plug into the new radio ( Mazda cable barrel is smaller than the port in the radio). I have been to a number of local auto stores in the area with no luck on finding this adapter, searching on line ( BTW:metraonline is a cool site) has not been any better. I e-mailed Dual radio but have not heard back from them on this. Now with all the Mazda Protege running around I thought this would be a easy part to find. Am I just over thinking this and there is a really easy answer (yes, I read the owners manual ) or do I need to visit a install shop for the part.

Thanks, Paul

Most of those antenna inputs are broad parts fitting a wide range of vehicles. I wonder if a 95-05 Ford antenna adapter would work http://www.crutchfield.com/S-GOHs32XH71E/g_119400/Antennas-and-Antenna-Accessories.html

Calling crutchfield would be my next step if there is no one helpful locally.

IME there are two sizes of Antenna connectors. As RossD suggests, a call to Crutchfield should point you in the right direction for an adapter.

Walmart has antenna adapters for just this reason. Go there, spend 5 bucks, and be done. That's what I did on my p5.