The long parts that are warped are a problem with alot of manufacturers, sadly. Running the resin part under really hot water will help some. The part can be taped to a straight edge of some sort, run under the water or quickly dipped into a pot of hot water and then cooled. If this doesn't work....toss it. The effort does not equal the outcome and alot of times I find it easier to scratch build the part from styrene, extra resin, metal or lately I've been looking at some of the aftermarket stuff.
I think I've had 3 swords that I could not rebend, and scratchbuilt them from plastic card stock. Spears, pilum, bayonets, etc I've made from extruded styrene or brass rod. Scribe the center of the blade of the sword and use it as a guide for a rat tail file to make the fullers on either side of the sword. Some sanding will make the diamond shape cross section of a sword blade. Rifles, muskets etc can be made by either fabricating a new one. Remove the barrel, leaving the stock, a replacement length of fine tubing will act as a new barrel and serve as a spine or straightener for the remaining stock. The locks , etc can be salvaged from the remainder. Copper or lead foil, or strip styrene has acted as bands securing the barrel to the stock. (as well as made nice slings). Usually and hour or so of work will yield a nicer piece than the supplied version.
I don't have it at hand, but I will look up the sources I have for aftermarket parts if scratchbuilding is not your thing.
Mike
"Imagination is the dye that colors our lives"
Marcus Aurellius
A good friend will come and bail you out of jail...but, a true friend will be sitting next to you saying, "Damn...that was fun!"