Some papers that are not easy to find
If you would like a copy of any of these papers, feel free to request access and I'll be happy to share them with you.
H. C. Grötzsch, Zur Theorie der diskreten Gebilde VII: Ein Dreifarbensatz für dreikreisfreie Netze auf der Kugel, Wissenschaftliche Zeitschrift der Martin-Luther-Universität Halle-Wittenberg. Mathematisch-Naturwissenschaftliche Reihe 8 (Nov. 1958), no. 1, 109–120 (German). MR0116320, Zbl 0089.39506
V. Neumann Lara, Seminucleos de una digrafica [Seminuclei of a digraph], Anales del Instituto de Matemáticas (Universidad Nacional Autónoma de México) 11 (1971), 55–62 (Spanish). MR0317987, Zbl 0286.05113
V. I. Arnautov, Ocenka chisla vneshnej ustojchivosti grafa s pomoshh'ju minimal'noj stepeni vershin [Estimation of the exterior stability number of a graph by means of the minimal degree of the vertices], Prikladnaya Matematika i Programmirovanie (Institut Matematiki s Vychislitel'nym Tsentrom, Akademiya Nauk Moldavskoy SSR) 11 (1974), 3–8 (Russian). MR0340103, Zbl 0297.05131
V. G. Vizing, Raskraska vershin grafa v predpisannye cveta [Coloring the vertices of a graph in prescribed colors], Metody Diskretnogo Analiza v Teorii Kodov i Shem (Institut Matematiki Sibirskoe Otdelenie, Akademiya Nauk SSSR, Novosibirsk) 29 (1976), 3–10 (Russian). MR0498216, Zbl 0362.05060
S. Negami, Classification of 6-regular Klein-bottlal graphs, Research Reports on Information Sciences A: Mathematical Science, No. A-96, Department of Information Sciences, Tokyo Institute of Technology, Oct. 1984, 16 pages.
M. Mirzakhani, A small non-4-choosable planar graph, Bulletin of the Institute of Combinatorics and its Applications 17 (1996), 15–18. MR1386951, Zbl 0860.05029