This a specialist area under the Leasehold Reform Act 1967 where holders of long leases can purchase the freehold which has to be valued through the Leasehold Valuations Tribunal.
A great way to do it is to get a group of you together and instruct solicitors jointly - although you will all have to bring separate claims, because you are (potentially) dealing with the same landlord, and can instruct the same solicitors and same counsel, thus keeping costs to a minimum. A specialist will deal with this no problem - I recently dealt with 26 cases of leases from 1583-1587 (which was a headache). Do you know who the current landlord is? If so, it's a whole lot easier.