In my world and opinion, seeking that last special component, to complete a build, is part of the fun/frustration/reward, That said, I never allow not having the correct component from keeping me off of the bike. My Legnano is a perfect example. I have been building and riding it for many years. I rode the bike, initially, looking like this...
Since then, I have stumbled across these Legnano components...
I know that some items are not original spec, but they are what I have now. Imagine my joy when I found a near new old stock crank set and original bottom bracket...

After years of seeking and installing, I am still on the lookout for more items. Needless to say, I do not allow not having the model and period correct component, to keep the bike off of the road. And, since the Legnano is now my primary rider (so is my Rocky Mountain), I decided to go with clincher rims, the same ones that came with the Legnano pantographed Campy hubs...
And this is the vintage road bike that graces the cottage roads, these days. I really like the feel and appearance of this old Legnano. The only way it would ever be replaced is if I find a Roma that I can afford...