Jim Summers recommended two battery suppliers: EM3EV and ElectricRider.
I discounted EM3EV because they don't have exactly what I need. They have a "Request a quote" option, but are located in Hong Kong and don't list a phone number on their web site. When developing a product, it's often important to be able to talk with someone on the phone.
ElectricRider has what I need. But, when I called the good people down in Texas and asked about a solar charge controller, they said their controller works on 120 volts and if my "solar panel puts out 120 volts, it'll work fine." *facepalm*
I consulted the great AI known as Google and found Bioenno Power whose "products are trusted and employed internationally and domestically by a wide customer base ranging from amateur model makers using our batteries for RC applications to professional aviators trusting our batteries to power critical avionics and Ham Radio operators." And, they sell solar charge controllers for their LiFePO4 batteries. Wow! Sounds like a perfect fit.
So, I called them. They were very pleasant and helpful, but insisted that 24 volt batteries need 24 volts of solar power. Inexpensive, small form factor, 100 watt (C/5-ish for 24 volt, 20 amp-hour batteries) pretty much don't exist.
Not to be deterred in my quest, I consulted Google a few more times and found a vendor in California that sells a device that does what I want. But, it's manual is in poorly translated Chinese, which doesn't inspire confidence.
So, I've decided to let go of my desire for a solar panel on my rover. This will allow for a smaller, lighter rover that isn't top heavy. I can charge the batteries from a pair of ground mounted 12 volt panels. I could use a DC/DC converter to step up the 12 volt solar panel to 24 volts for the charge controller. But, this is going past the design goal of "keeping it simple."
Moral of the story: follow your heart. It may not lead you to what you see in your dreams, but it may lead you to a better vendor of LiFePO4 batteries.