The only example I can think of (and this one is obscure enough to very possibly be a KASU) is a mention in #38 about Arbat 'selling' organs. Which doesn't prove too much, as they may have been using the word 'sell' instead of 'trade' simply because words don't always translate directly that way. But it's something.
As for the Skrit Na and the Ketrans, I don't think we know enough to know one way or the other. The Skrit Na are more of a scavenger race than a trading race, anyhow, so I could actually see how they might evolve without the concept of currency (ie, if you can just take what you want from some unsuspecting planet whenever you want it, what's the point of having an assigned value system for buying and selling such things?). Which might help explain the Iskoort situation, because they may have developed that same sort of opportunistic mindset as they were evolving, as well. And only came up with trading when it became obvious that you can't always take everything you want with no consequences.
For the Ketrans, your guess is as good as mine. The book never even goes into detail about what they look like, let alone how their economy works.
