The Rules About Wizards
As the wizard's Spellcasting feature explains, in the section "Learning Spells of 1st Level and Higher":
Each time you gain a wizard level, you can add two wizard spells of your choice to your spellbook for free. Each of these spells must be of a level for which you have spell slots, as shown on the Wizard table. On your adventures, you might find other spells that you can add to your spellbook (see the “Your Spellbook” sidebar).
RAW, if your Wizard gains a level, they get two spells, of their choice, for free. This means that somehow they found copies of the spells, and somehow they found enough fine inks to transcribe them, without paying anything and without having to worry about locating the copies or the inks. In your situation, that would be the bare minimum. If your DM wishes to play by the rules, she must make these spells and inks available to wizard characters when they level. Whether that simply happens 'off camera', or it has a narrative description that you play out, is her decision.
For gaining other spells, we look to the sidebar, which says:
When you find a wizard spell of 1st level or higher, you can add it to your spellbook if it is of a spell level you can prepare and if you can spare the time to decipher and copy it...For each level of the spell, the process takes 2 hours and costs 50 gp. The cost represents material components you expend as you experiment with the spell to master it, as well as the fine inks you need to record it. Once you have spent this time and money, you can prepare the spell just like your other spells.
From this, note that inks are not the only costs to copying a spell - there are also material components to expend as you experiment. But also note that these 'experimental components' and 'fine inks', while they do have a defined cost, do not appear on official equipment lists as something that characters can purchase.
If your DM wishes to play by the rules, she need not make these materials and inks available to wizard characters at any particular place or time. If she does make them available, that may happen 'off camera' or it may have a narrative description that you play out.
The Nature of Barovia
Curse of Strahd is a very atmosphere-heavy adventure. Being in Barovia should feel different from other places in your campaign world. Your characters, and you the players, should feel isolated, cut off, suspicious of everyone, and often like you are being manipulated. If one of the ways your DM is encouraging those feelings is through the material economy, that is well in line with the adventure guidance. It should be difficult to access inks in Barovia, because everything is difficult to obtain in Barovia. You may have to make some uncomfortable bargains with people you would rather not negotiate with, because just to survive in Barovia may compromise your principles. Some people may tell you that they don't have such things, when they actually do, because not everyone you meet in Barovia is trustworthy. They might even sell you what they claim are fine inks, when they are normal ones and will not work for spell copying1.
Spells are a source of power, and Strahd has a stranglehold on power within his realm, so you may end up dealing with him in a way you would prefer not to - or you may think you are getting them from a neutral third party, when in fact that person reports to him. If any of these things are your experience there, so much the better - your DM is playing the environment as intended.
At the same time, your DM needs to, if she wishes to play RAW, somehow permit you to access at least the spells, materials, and inks that are due you as you level. "There are no inks in the place descriptions" (and there aren't any, in fact) is not an excuse for withholding these.
Beyond what you are due as a function of class, she may allow you to find other inks and materials. But she should be aware that she needs to do so as a function of her role - "The DM describes the environment". She needs to make active decisions about where inks and materials will be available, because the DM always makes decisions about where inks may be available. She certainly can decide that there are none, but she needs to realize that is an active decision on her part, and not a consequence of them not being listed in the descriptions. A DM always needs to decide how available to make these inks and materials in their world, because in general they will not be listed. In keeping with the atmosphere of the adventure, but not severely hindering wizards compared to other classes, it would be appropriate to make these materials and inks difficult, but not impossible, to find. Any and all of the spoilered locations listed in guildsbounty's answer are reasonable places to find them, and I used more than one of them as such when I ran CoS.
1See, for example, location N9i where
Vistani may attempt to sell PC's 'magical potions' that are not, in fact, magical.