Where can I find statistics about count of words starting by letter?

Solution 1:

I thinks this might be what you are looking for, Scrabble dictionary statistics for 187630 words: https://www.unscramblerer.com/scrabble-twl-dictionary-statistics/ it has percentages as well as numbers for words starting with, words ending with and words containing all letters of the alphabet. There are also stats for word lengths.

English language obviously has more words than 187630, but they will get longer and more obscure.

Solution 2:

dictionary.com can be searched by letter.

The link I have cited has three pages worth of words starting with "z", and you will also be able to search words starting with "x" or any other letter of the alphabet.

Dictionary.com is an aggregating dictionary, i.e. it collects and displays words from various dictionaries. You will probably need to count the words manually though. There doesn't seem to be a total for each letter.

Dictionary.com is the world’s leading online source for English definitions, synonyms, word origins, audio pronunciations, example sentences, slang phrases, idioms, word games, legal and medical terms, Word of the Day and more. For over 20 years, Dictionary.com has been helping millions of people improve their use of the English language with its free digital services

Collins Dictionary Wordbank includes meta-data. It offers a free one month trial.