can I get battery for MacBook Pro (Retina, 15-inch, Early 2013)

While your laptop is considered "Vintage" an Apple Authorized Service Provider may still be able to replace the battery for you if the part is still available. An original Apple battery is the best option if it is still available since the quality of third party Lithium-ion batteries is extremely poor even when purchased from a reputable vendor such as OWC as @verdee2000 suggested. OWC is your best option if a third party battery is necessary.

where are you located..if in USA you can try hhttps://www.macsales.com;

elsewhere you will have to rely on local dealers; usually in India you can check with service centres run by apple dealers; they keep batteries and give you 1-3 month warranty as well.

Hope it helps..

Note that OWC, the vendor mentioned, recommends professional installation.