I love crossing things too, but you will get an adapted landrace without any crossing whatsoever just by saving seeds from your best surviving and most productive plants. Subspecies happen without crossing. I've grown Jamaican sorrel in zone 7 for example. 15 years ago the plants barely had time to even make pods before freezes and I'd only get one plant to even make a few mature seeds. Now this year and last all of mine make mature pods and seeds by june. My leaves are completely different from the original also. Beans are hard to naturally cross. I've grown beans side by side for decades and still have the original kinds. I hold fast to the fact that my beans have adapted to my region better each generation of seeds saved. If you only save seeds from the mother stallard pods with the most beans per pod you will have more beans per pod the very next year. I've done wonders in 26 years with a tomato variety I have. I just save the best tomato and from the best plant. Each year it becomes noticeablely better in every way. My tomato and my Jamaican sorrel are landrace to my region now. With crossing you get a hybrid, with time you get a landrace. Most important of all is simply selection of the mother plants. You will also find bizarre mutations you might wish to select for that just happen even in pure stock. I am 59 and grew my first beans at 4. I think rancho gordo has the best deals on beans but alot of them won't even produce beans at all in my area due to photoperiod I suppose. The only lima to produce in Alabama black eyed lima. You gotta find what grows in your area and tastes best and stick to saving seeds to get your landrace. If you cross your landrace then the next year it is very possible you will lower resistant traits and they will suddenly become prone to pests and sensitive the harshness of your climate. This happened in India when a large chemical corporation talked local farmers into investing in so called improved cotton. Thousands of local farmers committed suicide because of debt from crop failure.