Hardly any kana ligatures or polysyllabic kana are represented in standard character encodings.
History
Nobori banners in sumo, using the yori ligature ゟ
These characters were widely used until a spelling reform of 1900 decreed that each sound (mora) would be represented by one (kana) character. They were not represented in computer character encodings until JIS X 0213:2000 (JIS2000) added yori and koto.