Replacement Speakers

[Freddo]

My alternator went out and it took out some of the wiring inside the cab of my 1967 c10. (283 CI and almost completely stock)
While replacing the cab wiring, I thought I would deal with the old am radio. Since I've owned the truck, my radio functions, but the original speaker was unhooked and there were two small speakers hanging below the heater that the prior owner wired in. These are really difficult to hear and work intermittently.
I removed the radio and removed the original speaker. (I tried to attach pictures but it asked for a url and I couldn't figure out how to post them.) This original speaker measures 4 7/8" x 10 5/8" and is obviously worn out. I've searched the site for speaker replacements but only see 4 ohm upgrades which won't work with this old radio.
Here is my question:
Does anyone know where I can get a replacement for the original speaker that is a 10 ohm model? I would love to have it fit the original bracket, but am willing to do a little altering on the bracket if needed. I'm not upgrading the radio and don't need a high fidelity upgrade, but would like to be able to listen to the radio.
Thank you so much for the guidance in the electrical section concerning changing the alternator to a 12SI. It was a real help!
Thanks in advance for any guidance you can offer as far as the speaker.