There doesn't appear to be a painted version of the refuge tree described by the 17th Gyalwang Karmapa in Ngondro For Our Current Day... yet.
One of the beautiful things about thangkas, though, is that they can be commissioned. If you have an artist you trust, and who can follow the text carefully (most likely in the original Tibetan, taking His Holiness' commentary into account), I'd say that's the most sensible way to go. That is, if you can afford to become a patron of the arts.
Remember that thangkas are supports for visualization, and ideally should be consecrated by a lama so that they are actual representations of the deities depicted. When going for refuge by practicing the first section of the ngondro, try to visualize the refuge tree that Karmapa describes as best you can. It's pretty common to hear people say that even if your visualization is foggy or unclear, as long as you have confidence that the Three Roots are present before you, you needn't worry too much. The lamas know that visualization is difficult to accomplish in this degenerate age, so don't beat yourself up. We're not perfect, after all... otherwise we'd already be Buddhas!
Karmapa's description of the field of accumulation is very detailed and lucid. You have the book, so just make sure to familiarize yourself with his explanation and habituate yourself to it. The more you practice, the more easily you'll be able to call it to mind.
May all beings benefit!
"The Sutras, Tantras, and Philosophical Scriptures are great in number. However life is short, and intelligence is limited, so it's hard to cover them completely. You may know a lot, but if you don't put it into practice, it's like dying of thirst on the shore of a great lake. Likewise, it happens that a common corpse is found in the bed of a great scholar." ~ Karma Chagme དྲིན་ཆེན་རྗེ་བཙུན་བླ་མ་རཱ་ག་ཨ་སྱ་མཁྱེན་ནོ།