Block from U+A960 to U+A97F. This block was introduced in Unicode version 5.2 (2009). It contains 29 codepoints.
The Wikipedia provides the following information on block Hangul Jamo Extended-A:
Hangul Jamo Extended-A is a Unicode block containing positional (Choseong, Jungseong, and Jongseong) forms of archaic Hangul consonant and vowel clusters. They can be used to dynamically compose syllables that are not available as precomposed archaic Hangul syllables in Unicode containing sounds that have since merged phonetically with other sounds in modern pronunciation.