i wouldn't buy new, i would clean the ones that you have. that get noisy when they get clogged up inside with old oil and new oil cannot get in to close up the gap between valve head and cam.

take them all out and soak in degreaser. if you can put them somewhere warm (80 degrees is good), it's much better as the oil will get thinner and come out easier. what you're aiming for, is for the plunger in the centre to be easily moveable with your fingers. you'll find that on some that you remove, you won't be able to push it in as the little hole is blocked.

put the tappet in a vice or clamp, with a piece of ally tube on the plunger and slowly start to compress it. the old thick oil will be gradually forced out of the hole. do that a few times, and put back into soak. when in soak, push the plunger in and out to allow the degreaser to be sucked into the tappet (air bubbles will come out). do this as much as necessary until all tappets have free plungers that go in and out easily against the spring.

when you put them back in, they'll be lovely and quiet. if it is tappet noise that you have, and not little end bearings