Some mention of the potential of Desmanthus leptolobus has been made here and elsewhere. From what I can tell, it's similarly resilient in terms of climate compared to it's cousin, but easier to grow. I do wonder about the resilience, however, considering where it's found:
http://plants.usda.gov/java/profile?symbol=DELE2Besides the relative ease of cultivation, it's said to have a higher and more consistent alkaloid content. What I foresee--assuming this info is fairly accurate--is that a large number of plants could be brought to some level of maturity indoors rather quickly through use of hydroponics, then be planted outdoors to give the roots some room.
I'm of the opinion that all the common sources would take too long and be too troublesome for most people to grow, considering space and climate. I also think that the various grasses contain too little alkaloid content or yield too inconsistently to be feasible except in terms of wild-growth and as a sort of last-ditch effort--worthwhile to research long-term, but probably not suitable for current concerns.
If hydroponic methods are suitable, it could make a great companion for
Trichocereus, allowing the same sort of setup to be used in cultivating sources for two of the most relevant entheogens of our time, thus securing their future. The keys to the success of this are high yields (number of plants, speed of growth, alkaloid content) and accessible/reproducible cultivation teks.
As a start, anyone with access to live samples should either make them available and/or test them to ensure that it's a viable source, as this would save a hell of a lot of time and possible disappointment for the whole community.