Unfortunately it can be frustrating to get farms to spawn in the game as sometimes it may just decide to instead just build Light Density Industrial buildings instead of Farmland (and it can get annoying).
The only things I can suggest is to:
1: Try and build it within the first 5-10 years of your city.
2: Enact the Farmer's Market Ordinance. (This increases the chances for farms to spawn.)
3: Build it far away from the rest of the city, but not too far that it makes the farms abandon quickly from a lack of viable transportation methods.
4: Make sure it is a large Light Industrial Zone (I can't remember specific sizes).
5a: I think they may be more likely to spawn if you don't connect the zone to water at first. I'm only basing this off the fact that zones do not need water for buildings to begin spawning in zones; they only need to be powered. After it spawns, then you should be able to connect it to water.
5b: If water is needed, then I would recommend it use its own source of water (It is Not connected to the pipes that are used by the city.), otherwise water pollution from the city's pipes will spread into the zone, which will cause the farm to become abandoned. ALSO I DO NOT recommend it being connected to a nearby Water Tower, as those have a side effect of increasing nearby land values. If you prefer a water tower, do not place it too close to the farm.
6: They will not spawn if there is too much pollution in the zoned area.
7: Add a method of Mass Trasportation that IS NOT a Bus Stop in order to reduce traffic in the nearby roads.
8: Place it in an area that has very few or no trees to keep the land value down. If the place you want to put it has trees, then you are going to have to remove them.
9: After you manage to spawn a Farm, query them, and toggle the Make Historical so that in the chance that it gets temporally abandoned, it doesn't get immediatly replaced by Industrial buildings.

I'll make another post if I find any more tips from the iOS port of the game (It is known as SimCity Deluxe. It is essentially SimCity 3000 Unlimited, but with some minor and major changes. I'll list these differences in a later post if you want to know. Unfortunately, I think it may have been taken off the App Store around the time SimCity 2013 launched).