You could contact PSI via their website and ask if you can buy tools from them. I doubt they would sell you EOI stickers since it requires a PSI cert # to purchase them.
As for the hydro after tumbling; they say that its not necessary to hydro just because the tank was tumbled.
If you saw something of concern after the tumbling, then it might be a good idea to have the tank hydro'd. If a tank is tumbled to remove light rust and resulted in a clean tank with no concerns noted, then it would seem to be a little overkill to require a hydro.