It seems that straight American Sycamore, once it gets past spring anthracnose, has nice, deep green foliage until fairly late in autumn. However, London Plane, at least the commonly planted Bloodgood, around this time every year, is turning yellow brown with significant leaf drop for some reason, I think a combo of the stress of the sycamore lacebug and powdery mildew, but that's just a WAG on my part. Do some of the newer LP cultivars like Columbia, Ovation, and Exclamation avoid this issue?

It is propagated by cuttings, so you won't get seedlings anywhere. They're all cultivars, even if the cultivar name isn't specified. Resin

There are several really decent varieties developed by Dr Lambeth. Mosage is another one.

Bill, As a hobbyist, you are doing fine and there is no constraint as to whatever you might attempt. My one concern, and it is a niggling one, lay with any future offering of Avlanche for sale, say by Mr. Fausett. In that case, I would prefer, and indeed would only be comfortable, if the plants had been vegetatively propagated from true-to-name mother plants [for many of the reasons stated earlier]. As a nursery business, overwintering, space, insect/viral infection and similar issues would not be a concern for him. What i want to stress, without inadvertently being discourteous or tactless, that in a commercial situation, one cannot make a cross from a pedigree and name the outcome to be the same as Avalanche. And, especially, sell that progeny as Avalanche. One could sell it as "the same cross that produced Avalanche" [truth in advertising]. Had the two parents been maintained as highly inbred lines, assisted by tester lines, then, certainly, every cross of that pedigree would be a modern F1 hybrid. Not quite so for two OP parents. The reason I go to such nitpicking detail is that I have worked on the physiology of flowering, parthenocarpy, the earliness gene, membranes etc. for tomato since 1984. For the past several years, i have crossed and recrossed several large-fruited and cerasiformae, observing interesting linkage and drag effects that are quite unwanted with the trait of interest but exceedingly difficult to get rid of by conventional methods. I am not a plant breeder by a long shot, but have a lifetime passion for the yield physiology, growth and development etc. of the large-fruited tomato. So i completely share your passion, and wish that excellent outcomes like Bwine OTV happened far more often. I have some careully calculated crosses going each year for 1 trait, the results are usually interesting but not what i was hoping for! Good luck! g