Leather conditioner will be sold in any good tack shop. You will also be able to search "leather conditioner" online and find brands sold where you are.

Here a common brand is "Lexol". Lexol sells both leather cleaner and leather conditioner. Some leather conditioner comes as a liquid in a squeeze bottle, some kinds, like saddle soap, come in a jar with a circle of cloth as an applicator.

Maybe I am lazy, but I like the varieties that come as a piece of cloth already impregnated with the conditioner--sort of like a leather conditioner "moist towlette". I find that the towlette style keeps me from loading the leather up with two much conditioner...but that's just me..