There is no plan to offer base L5 motherboards AFAIK, but there is a plan to sell bare Liberty PCB upgrades. The store page has just not been created for them yet.
(…but honestly, buying a spare refurbished L5 is cheaper than buying the Liberty PCB upgrade at this point.)
I previously proposed offering a category of replacement L5 components in the store, but this pales in comparison to some of the other priorities coming up, so it may take some time.