where is the BFG found in the game?
is it possible to get the quad damage thing in the fan map?
if so how would you go about getting it?
None of the included Open Arena includes the BFG, for obvious reasons. Except on one CTF map.
However, if you want it, then start a server yourself (or find one with cheats) and enter /devmap map <name-of-your-map> and then /give all.
This should give you access to all weapons.
The Quad in fan is reachable if you perform a rocketjump (easiest way), simply point your aim in the ground, jump and fire a rocket at the same time.
Some steering, some practice and Bob should be your uncle..