Explosive fastball

what/where is best to farm for fastballs and can someone help me get a level 72 explosive fastball

There is no designated drop source for the Fastball Grenade. Boll was supposed to drop it but does not, and it doesn’t look like that will ever be fixed. Your best bet for farming might actually be the How Marcus Saved Mercenary Day DLC, since you always or almost always get 4 grenade mods from the Loot Train and there are 2 other Red Chests in the area as well that could potentially give you the Fastball Grenade.

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I got the fast ball from farming the dragons on tiny tinas raid

I got one from Mortar, who respawns by the elevator once you’ve completed the main story mission there. May have just been lucky, although I know I have a couple of Fastballs at different levels in my inventory.

I have seen Loot Midgets dropping Fastballs and in the Captain Blade’s treasure room.

Of the Fastballs I’ve had/have they’ve all come as world drops from LLM- you could also ask for one in a trade (I just gave away am OP8 Explosive Fastball a few weeks ago…).