The original relay is common as dirt. It's available at any auto parts store. But not by a JD number. John Deere makes most of their engines but not all. It doesn't make relays. Nor do other engine makers. It is made by a specialty company. Probably in China now.
This relay was used on cars and equipment from the 1940s. Cars, tanks, tractors, even aircraft, anything needing a 12v starter relay. Some versions have fewer posts. Some have a button in the end to bypass the key. Handy in an engineroom to jog the engine.
Auto parts stores have a catalog with pictures. You pick the one with the right number of posts and amp rating. $20-40 on ebay.