Concerning your suggestion of wanting to take over someones existing rental that is likely to be a difficult approach for a few reasons.
(i) the existing people will need to be able to do the exit interview with the owner/managing agent and get their deposit returned.
(ii) the owner reserves the right as to who they rent to and will want to check references etc, if you haven't arrived in the country they have limited guarantees you will arrive and be financial. They may want to even rent to someone else and they actually have every right to choose to do that and as the risk of someone already here and able to be checked out is easier.
(iii) have you got either an employers reference or a gemeinde financial record to prove you have no history of debt
(iv) If you are planning to take over a lease sight unseen then there is a good chance any damage will end up your responsibility after you move in if the prior people dont mention it.
If you are looking for something coming available at the time use
www.homegate.ch as it sometimes shows when a place is available from.
The most likely situation is someone may be able to nominate you as the replacement tenants to move in if they are leaving outside the regular notice periods which are typically 6 months interavals at March and Sept each year. This would allow you to negotiate with the owner so that the prior tenants are released of their obligation to pay until a new tenant is found. You can then negotiate if the owner wants the same rate of rent or increased amount to what they were receiving.
PS: In most cases remember to bring your lights to instal aas the prior people need to take the existing ones with them usually.
This info may give you a little help,