you might want to consider sweet seeds afghani S1's.
if you buy those beans they should be extremely stable. an S1 bean is virtually a clone in seed form.
S1 = a female plant pollinates ITSELF. (by using colloidal silver or some other method to unnaturally produce "male" pollen)
so therefore all the offspring should be virtually identical.
This is a common misconception, one sometimes promulgated by the ones selling ceeds, but its simply not true.
S1 plants are NOT the same as clones in ceed form, and not even close. If this were true, there would be no such thing as "clone only" strains, right?
Exactly as you say, an S1 is a sexual cross between a plant and itself. (Often pro breeders will cross one chemically treated clone of a plant with another from the same the mother plant, but it amounts to the exact same thing).
Now *IF* (and only if) the mother plant is a plant from an inbred line, then the feminized offspring will be similar to each other, and similar to the parent, the same as a sexual cross between any male and female plant from the same inbred line.
But if the mother plant is a HYBRID (which includes many popular strains and most of the "clone only" strains), then you've got the equivalent of a sexual cross between two F1 hybrid plants. Now your feminized offspring S1 ceeds will grow into plants with a wide variety of phenotypes. Not only may they NOT be similar to the mother plant, they probably won't even be similar to each other.
In this particular case, the Sweet S-eeds afghanis may well be inbred, so the S1s could be similar to the parent. Don't really know, but it would be a mistake to assume that they will be unless you know the parent is stable.
If you want to see/hear more about S1s, check out my grow report on Sickmeds Green Crack S1 in my signature.
Also, getting back to the original question, if you want to see a good example of a true inbred line, check out the Sickmeds William's Wonder grow in my signature too.