You can get things like Grape Seed Extract in powder form which should work as well as berries. I do recommend the berries because the pigments Proanthocyandins/Anthocyanidins strengthen/reinforce the blood vessels, arteries veins, skin and even bones.
You should be able to find a source on your continent. I have been using>
GSE if you encapsulate it might be okay with your tongue. It is probably best encapsulated as I take it myself but have been adding 0.5ml scoops mixed with other herbs in water and it is terrible taken with water as it tends to stick to the teeth discolouring them. It's removable but a bit of a nuisance and I am thinking of using capsules myself. I have been thinking about purchasing an encapsulation machine anyway because I do use powdered herbs and it's time consuming doing it manually.
Vitamin C I would say is essential. As much as possible.
Smaller quantities of Vitamin C, no strict quantity but around the 4000 mg type of dosage, does tend lower histamine but when the dosage gets to around the 4000mg level it can activate macrophages and increase histamine levels. Therefore smaller and more frequent dosages might be more helpful.
BTW there are stomach infections which encourage the production of histamine!
It might be worth looking at Traditional Chinese Medicine as they use tongue diagnosis and if you look at tongue charts it might help indicate why you have your tongue problem and where the problem lies. I have noticed patterns on my tongue myself at times.