import re

regex = r"\S+(?= \(KM\))"
strings = ["261.30 (NM) / 300.76 (MI) / 483.93 (KM)", "952.27 (NM) / 1,096.09 (MI) / 1,763.61 (KM)"]

for s in strings:
    matches = re.search(regex, s)
    if matches:
        print(float(matches.group().replace(',', '')))