As others have said, they're not used in modern Japanese and the characters aren't taught in Japanese Elementary schools. However, saying they don't exist isn't technically correct; they do exist and are used in very rare situationsan old textbook on Wikipedia. You You can find them here: ヤ行イ
Links to the specific kana charts for reference:
- https://ja.wikipedia.org/wiki/%E3%83%95%E3%82%A1%E3%82%A4%E3%83%AB:Tuzurizi12.jpg
- https://ja.wikipedia.org/wiki/%E3%83%95%E3%82%A1%E3%82%A4%E3%83%AB:Syougaku11.jpg
This Yebisu beer is as an exampleEdits: I misread the question originally and missed the specific context of modern usage"yi" look at the katakana character after 琥珀: , "ye, "wu". I don't know a modern specific situation where those have been used.