Suit Supply has a wide range of sizes, fits and modest prices (for a suit). But if you are thrifting, maybe that is out of your range. The truth is that suits are expensive, and people who do not conform to standard sizes often need to resort to custom made garments, which are not cheap, in order to find a great fit. This is especially true if one has special needs in the shoulder area, since shoulders are so difficult to alter.
Best of luck.