For the the Sandman ball, if you want to give it infinite ammo, you might want to play around with the hidden cvar " tf_scout_stunball_ball_regen_rate".
I don't recommend setting it to 0 as it effectively gives scouts a stunball minigun. Also, large numbers of balls rolling around will make clients and the server lag.
Here's the list of scout cvars I got the stunball one from:
Linky
Just FYI there is another infinite ammo plugin by
twistedeuphoria (
linky), however a lot of times it bugs and has to be manually reloaded.
Also it doesnt quite work for the pyro as (s)he runs out of ammo after a while.