In case of late 70's - early 90's 38/357 revolvers, what are the most important spare parts to have ?

I would recommend hammer noses and their associated rivets.

Extra rebound spring, extra firing pin, extra main spring. That's all I've needed in my shooting bag.

I would add, an extra hand, already fitted. I had the hand pivot pin break off during a match one time.

The only spares that I will always have is the bolt return spring - it is so small that I tend to lose it. Since I am an inveterate tinkerer, I am inside my working guns pretty often. I know that there are some that don't agree with that, and in principal, I agree with their perspective when it comes to your collectible guns.

I assume that you are asking with respect to a working gun, which I treat differently than a gun that is more of a collection piece.

I have never had a hammer nose break, but I have heard of it. Now that it is mentioned in this thread, I think that a nose and rivet will be in my toolbox from now on.

Some do not use care in the breaking down a weapon.

A spare Extractor rod is nice to have if the end get chewed up.

Maybe a second set of grips.
One for carry and one for range work, if you like ?

Small hide away grips are not always the best for accuracy, at
least for my range and field trips.

Perhaps side plate screws. I've not yet lost one as I'm paranoid about it happening some day.
All these decades shooting the heck out of my revolvers and I have not needed to replace a part. If your competing I do understand the need though. Otherwise parts can be ordered if needed.

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"from my cold dead hands" C.H.

Hammer noses are a lot harder to come by than they used to be.

I tried ordering some from S&W several years ago, and they told me they had none to sell. Same goes for the "pivot-rivet" for the hammer noses.

I found an outfit in Canada that sold me some. The parts were used - even the pivot-rivets.

Gathering a small supply of parts is probably still a good idea.
Complete spare guns (of the type you truly actually use - not just that you "accumulate") is probably an even better idea.

Two is one.

One is none.

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WWSSD?
What would Skeeter do?

Unless you know what you're doing, the only spare parts you need are springs, a hammer nose and rivet. In most cases, you cannot just interchange revolver parts, the need to be fit by an experienced armorer or smith. The parts in the lock system all work with each other thus, they must be fit to interact correctly or to just fit in the frame. When working on a revolver, I had to use parts large enough to fit to other parts. As an example, the hand and the extractor must be fit to each other to properly rotate the cylinder. As this is happening, the cylinder stop must be fit so it doesn't bind when the hand is rotating the cylinder. Side plate screws are Ok but the one holding the yoke in must be fit!
End of story, most parts are not interchangeable unless you just get lucky.

I think I know the place you're talking about in Canada, I ordered a couple of sideplate screws from them awhile back when S&W was out.

Depending on your shooting, you might want to get a spare barrel for your .357 magnum K-Frame.

The springs I haven't worried about, they seem easy to find (although please correct me if they've gotten rarer all of a sudden).

In the meantime, I'll just keep getting more "spare guns", I have to have a source for parts right?

been shooting revolvers for 55 years and the only spare parts I have ever needed were more boolets!

Bear