How large must a word list be in order to have a reasonable chance of including words starting with every letter of the alphabet? Because word starting with X are far less likely to occur than others, this question essentially reduces to the probability that a word list of length n contains one or more x-words. If one draws at random n words from a much larger list in which a fraction p or more x-words, then this probability is equal to 1- (1-p)*n, where p*n is p raised to the nth power.
Eckler, A. Ross
"Word Lists With All Starting Letters,"
Word Ways: Vol. 38
, Article 17.
Available at: http://digitalcommons.butler.edu/wordways/vol38/iss2/17