Here is a list of some DC-DC converters that are available:
DC%20to%20DC%20Voltage%20Converters%20-%20DIY%20Solar%20Panels%20&%20Renewable%20Energy%2 0@%20AltE%20Store]DC to DC Voltage Converters - DIY Solar Panels & Renewable Energy @ AltE Store
It looks like there may be a couple that might fit your needs.
If not, here is a list of solar charge controllers and some of them have a stepdown function.
MPPT charge controllers for solar panels systems @ AltE Store
I am not pitching this vendor, they just have a large selection.