Please let us buy skill and support gems from a vendor in campaign

You can buy whatever you like in the Campaign.

You get access to Ange in Act 4, and before that you can teleport to the hideout of anyone who is selling something from their Merchant tab (Instant Buyout). They'll have Ange unlocked and you can use her Currency Trader as you normally would.

I really need this.
I don't have any support gem !
The fun for me is not to follow build guide but to try thing and I can't do it.