Pronunciation of 一 in 一边
Yìbiān would be correct.

For ordinals, it is pronounced yī. In other cases, When followed by fourth tone, it takes the second tone (一对, yí duì). For all other following tones, it takes on the fourth tone.

The reason it is not marked in dictionaries, is because the rules for tone sandhi are few and straightforward. Isolated cases are when a tone is dropped (or replaced by the fifth neutral tone), and those cases are usually indicated.