I found an internet reference that places King's Pony Farm between N. W. 105th and 107th Streets on the west side of N. W. 7th Avenue (US 441). According to one writer it had a background fort with a lookout tower that kids could climb up in. It is believed to have closed in the early 1970's. It is reportedly now a discount Value storage facility.
There is still an active Florida corporation with the name of King's Pony Farm, Inc. See http://www.corporationwiki.com/Unknown/Unknown/kings-pony-farm-inc-2674231.aspx