letters_a = ''.join(str(tup[1]) for tup in a)
letters_b = ''.join(str(letter) for letter in b)
regex = re.compile('(%s)[^%s]*(%s)[^%s]*(%s)' % (letters_b[0], letters_b[:2
    ], letters_b[1], letters_b, letters_b[2]))
match = re.finditer(regex, letters_a)
results = []
for m in match:
    first, second, third = m.start(1), m.start(2), m.start(3)
results.append((a[first][0], a[second][0], a[third][0]))
print(results)
How to perform search on a list of tuples