I made a pqb of all (hopefully, if there aren't any mistakes) number plate province + letter combinations. If anyone is interested the file is attached. Pleco treats look-up very well. Today I saw 吉A, 粤V, 冀J, 豫A, 苏C, 鄂A, 川K and 浙J - all I needed to do was search the pinyin: i.e.: ea (for 鄂A) and Pleco throws the results up immediately. Feedback for bugs, errors, etc. is welcomed.