To my knowledge there are no dedicated aftermarket parts on the market for any plastic sailing ship kit. The manufacturers, I suspect, figure the size of the market just won't justify such things - and they're probably right.
The good news is that several companies (the biggest American ones being Bluejacket and Model Expo) sell generic components for wood ship models, and those parts work just as well for plastic ones. That's where lots of plastic sailing enthusiasts get such things as blocks, deadeyes, and belaying pins. But if you want to replace such major components as masts and yards, you're going to have to make them. Either of the aforementioned sources can sell you some dowels to start with - as can woodworking supply firms like Woodcraft, Lee Valley, and Constantine's. Beyond that, you're on your own.
I built the big Revell ship kits (the Cutty Sark, Kearsarge, Constitution, and their clones) quite a few years ago. I personally didn't have any serious problem with bending spars; as such things go the ones in those kits are actually pretty hefty. And the rigging of a sailing ship is designed so that the pull of a line in one direction is compensated for by the pull of a line in another direction. On the other hand, I've heard lots of horror stories about poor quality control in recently-manufactured kits, including complaints about low-quality, rubbery styrene. Depending on when your particular kit was squirted into the mold, it may have problems that the ones I built didn't have.
Good luck.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.