After playing Plant Tycoon a LOT, I've found that there is Always more than one way to make each type of plant (of course except for the ones you can't breed like spotted).

So even if you don't have a citrus ball cactus (or any other plant you're 'supposed' to have) there is a way to make the magic plants. It involves some trial and error (and a bit of note taking), but I wouldn't give up just because you don't seem to have the right plants to breed with.

I have made up a foliage chart for myself as I've played and in a round about way you can work out which plants to breed with which (there are Hundreds of combinations of plants and flowers, and each two create another unique set of plants and flowers, so obviously there is not just one way to make any particular plant).