cuttin' quartz
You can still buy channel elements, but you'll need to retune the rig if the new channels are much removed from the old ones.
I had an old Micor mobile rig I retuned for marine band freqs...I used it as a 'base' for when my folks were out in the boat. I was 5 miles inland on a short stick on the roof of their house, and I could talk to them 5 miles up river.
When I tuned it, I tweaked the PA around the couple of freqs I did have, and got 130 watts out of it...LOUD!