I have two very very large sulcartas who will eat dandelions above and beyond anything else on the planet BUT I cannot grow them

I have tried everything I can think of - compost, manure, growing in pots, in the kitchen, in the greenhouse, outside in the garden, under a cloche. With/without manure, plant food, compost, peat, begging and even the odd swear word. Have tried virtually every means of growing stuff I can think off. I have brought seeds from umpteen different places, collected them from wild and even dug up full grown plants from my next door neighbours garden, and still nothing survives or grows. Should mention both my neighbours have gardens full of them but have dogs using garden as a toilet. So prefer to not use these if possible (I have almost an acre of garden and several thousand plants and large vegetable garden I have grown, all of which grow like jack's beanstalk except dandelions!). Does anyone have any ideas.
Have to mention I have a few small ones that start to grow in one flowerbed but they always die/disappear before they actually get any leaves or growth more than couple centermeters.