probably not what your looking for but while reading through your post, I couldnt stop thinking of this answer, I used to be a drag king (girl dressed like a guy etc etc for shows) and having 38D a bra was completely pointless so with the advice of a FTM friend I started using chest binders, the one I use still leave a slight bump but they actually look more like pecs and can only be seen from the side, dark colours completely cover up, I think this is the site I got mine from, but it was a very long time ago now, I mean like 4-5 years, so maybe do a look around just incase my memory is lying to me! http://www.t-kingdom.com/

*EDIT* that was not the site, I found the real site but they have shut down it seems but you can use the site I gave you as an idea what im talking about