Ebay and Amazon, but I haven't found the blanks to be any cheaper than buying PSI Ben's Best scrapers. I just get the cheapest version of the width/thickness I want and grind to shape. Thickness is listed in the specs, and they are pretty thick. I have a set of Rc hardness files and find the steel to be over Rc 60. Rc 65 doesn't really seem to scratch it either. They come with a tang so no need to grind that, and with a handle if it suits. Finding some hss pieces at the various places others mention is another option. You might consider a scraper tool using a mild steel bar with hss tips that attach with screws (smaller scraps could be shaped into various shapes - the challenge is drilling the hole. I have a carbide drill bit I have used for this)
As to comparisons of different steels - not sure what you mean by "observe", but I have looked for actual controlled tests (vs opinions of turners using them or mfrs claims), and have only found one, attached below. It is dated but the steels haven't changed. The edge holding benefit is there, just not to the advertised level.
Benefit of steel type (edge holding) depends on how the tool is used.
@robo hippy uses scrapers to rough with, so longer lasting edges are very important to him. I use other tools for heavy material removal, and use scrapers mostly for minor shape refinement and sheer scraping. M2 works perfectly well for me, and the lower cost allows having more tools of different shape, thickness, etc available for different applications.