Listing a model number will allow narrower results (whether it has a field coil or not). Otherwise www.tubesandmore.com sells many types of speakers that would do the job. You don't want a fancy one with a big magnet and a rubber surround. All you want is an all paper unit with good flexibility for bass response. If the radio is a small one, you will have to worry about the speaker fitting into the radio, especially if it goes right up against the chassis, perhaps by IF transformers and such that would cramp room. You can purchase one with a rubber surround if you wish. It will sound good. Radio Shack used to sell speakers, but they are discontinuing speakers. If you find some, they may be at good prices. They usually have the big ceramic magnets, though, which is undesirable for a small cramped radio. You can also try Quam, which manufactures speakers and has for many years. They may even have an exact replacement for yours. I think they have an internet address, but I'm not sure. Search under "Quam speaker." Keep in mind that they make a lot of speakers for public address systems. Usually these speakers have adequate bass response, but I have purchased some that were very stiff and only suited for speach reproduction. I think I even purchased a 5 inch one from them. It had a square old-style Alnico magnet.
Remember that if the radio means a lot to you and if the original speaker still exists, you are far better off getting it reconed. You must be firm in your orders when you take it in. Some incompetent places will rip the cone out of the speaker and then find out that they can't obtain a new cone or voice coil that fits. If they seem shady, try to purchase a 5 inch paper cone from them and then recone it yourself, using the original voice coil--if it is in tact. Be firm, though, and don't let them mess with you. Don't hand them the speaker until you are confident in their service. Some places are excellent, but I've come across some places that are a joke. They see that your speaker is old and because they hate old equipment, they will not be of very good service to you.
Thomas