If you have a sickle sharpener, getting the sickle in and out, is more of a chore than sharpening it. I try and sharpen mine every few years, but, I'm only cutting in a 4 acre field, way less than most make in first cutting. Like any other tool, they work best when sharp. What I have, is not exactly high tech. It's a mandrel, with a sickle stone, powered by a 1/3 hp electric motor, mounted on a approx. 5' 2" X 10". You basically stand it nearly straight up, and clamp it to something, then free hand, sharpening the sickle. Generally 4-5 light passes on the stone gets a pretty sharp edge. And these are bottom serrated knives.
I've replaced the knives on it only once, but had the knives on hand, picking them up at farm auctions over the years. All I had to do was buy the bolt kit.
But, I also have a spare sickle on hand, for just in case. Anymore, by the time you buy the knife sections,and bolts, you can nearly buy a new complete sickle, ready to plug & play. I have bought 2 through Webb Sickle Service, and they seem to be of good quality. I did break one a few years ago, but that was probably my fault for not sharpening it. The first cutting was pretty heavy, and tall, and wet underneath too. It is Rye Grass,and it was as tall, or taller than the fenders on the tractor, and it has 15.5-38's on it, so over 5' tall. I had to put the 656 in first gear to get through it, as it was all the rolls wanted to handle going through them. The sickle broke about 3/4 of the way through that field. Headed for the shop,and put in the spare sickle, and was back in the field in less than a half hour.
I've attached the link to Webb's below, but do what you want. It looks like the sickles for the New Holland are pricier than for the old IH, but, even at that, it looks to be about $70 more, than just a box of 10 knives. and every thing is new, ready to put in. You can put the new one in, then sharpen the old one, or put new sections on, and have it ready to go for a spare.
New Holland M/C: 472, 477, 478, (7'); 479, 488 and 1469 after SN22 947 (9'); 49 after SN259714 (12') - Ford New Holland - Sickles by Brand Webb Cutting Components