I would do this:
(only AFTER approved, not before)

Dear Beautiful Lady,

    I appreciate you checking my refs and agreeing to see me.  I normally would not discuss this.  Unfortunately, it has been a problem for me in the past.  I am hoping you will understand.  My length and girth are a little larger than most.  This is not an effort being made by me to brag.  I am hoping my size will not be an issue once we meet.  Sorry to be so explicit.  However, I thought it may be worth mentioning.  Please let me know how you feel about this.  

    Thank you....Sincerely, Hobbyist

I know it sounds a bit wishy washy.  However, sometimes you have to be very careful how you put things until someone gets to know you well.  At least this way, you have made your point without being offensive.  

Take Care and Stay Safe....Betty xoxo

DAYUM!!! We should get together ;-)

I can only speak for myself on this subject...but if after I've screened the gent and we have established a comfort level, I don't mind them mentioning a special condom request. If you were to say, "Paris, could you please be sure to have some XXL Magnums (or whatever) available..I'd appreciate it." This tells me that you're a man with an above average cock size.

Really...providers actually decline a gent for his cock size? I can understand if you're wanting greek...BUT...wow!