Do you know the measurements of a suit which fits you properly? Use this method: http://askandyaboutclothes.com/clothing/style-tips/how-to-measure-a-jacket
If so then give ebay a shot. You mentioned that someone is selling some HF suits in your size. I would suggest that you stop thinking of a certain number as your size. For example, let's say you bought a new unaltered Brooks Brothers made in USA 1818 Madison suit in 44R. It fits with only minimal alteration. Cool. You are a 44R, right?
Then you see a new unaltered Brooks Brothers 1818 Fitzgerald 44R on ebay. You snap that baby up, because it is a nice suit and it is your size. But when you try it on there is a bit of a problem. That Fitz is tight. It's tight everywhere; across the shoulder, at the upper arm, in the chest, everywhere. Guess what. You need a 46R in Fitz.
This is just the tip of the iceberg as far as examples of "knowing your size". BB suits which are manufactured in Italy are slimmer and smaller than the US made suit of the same size and cut, so not even every BB 1818 Madison will fit you.
And then you must consider that most used suits have been altered. You will see many suits on ebay which have a chest measurement which is actually smaller than the labeled size (it should be larger to allow for movement).
TLDR: Only buy a suit, blazer or sport coat on ebay if you know your measurements and measurements of the jacket are provided by the seller. Jacket "sizes" are not standardized and will often be misleading.