There is one replacement battery in development, by Fenix Power. There is another startup making the hardware to allow Leaf battery swaps between different generation Leafs. There is not currently an aftermarket replacement battery available for immediate installation. Your best bet would be to find a good used 12 capacity bar battery in a salvage yard and install that. If you have to pay someone to do it, you are looking at roughly $6k to go that route, depending on the cost of the used battery and the labor cost.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
BAFX OBDII Dongle
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.