"Do all of your heads deliver 2.5gpm?"
Yes, at 80 psi all do (unless it specifically states otherwise). If your house has less pressure than 80psi (while the head is operating) then you might get less volume than 2.5gpm.

"Do you sell a shower head with an easily removable flow reducer?"
Due to Federal energy savings laws we may not sell a shower head where the water restrictor is "easily removable."

"Does the showerhead I ordered swivel, or do I need an additional part for it to do so?"
It is rare for a showerhead not to have a swivel feature unless its position adjustment is in the shower arm or it is a "flat" model that is meant to be installed parallel to the floor. With the exception of those mentioned, some industrial models and most handshowers, standard-style showerheads generally come with a built-in swivel feature.