The seller needs a receipt from an FFL, to show to his local licensing office where the revolver went when it was sold.
They use that to delete the handgun from his NYS Permit so he is no longer responsible for it.
(In state sales between individuals are allowed in most cases but require a notarized receipt,,but that's a different issue)
Having a local gunshop in Buffalo handle the transaction would take care of it very easily.
The Buffalo Gun Center on Harlem Rd would most likely handle it. They are about the largest in the Buffalo area.
http://www.buffaloguncenter.com/index.html
He does need a receipt from an FFL to show where the gun went. That receipt (and license copy if for some reason he ships it directly out of state) is needed to give to the local licensing authority (Erie County (Buffalo,NY) Clerks Office I'd assume in this case).
They'll then delete the revolver from his NYS Permit so he's no longer responsible for it.
An FFL doing the transfer will give him the receipt and necessary paperwork needed to delete the gun when he drops it off for shipment. They have to log it in from him, then out to the FFL in NM.
Before shipping it himself to an FFL in NM (if he chooses that route), he should check with his Clerks Office,,as some do not accept the receipt and/or license copy of an out of state FFL as proof of a sale unless both partys are FFLs.
Others do,,,it's a fine system!