is there a way to get access to a number of empty seats at different airlines? how do I get this data?
Edit: my question is if the OTA's have this access? do they know at every moment how many tickets are left in each class? do they get this data from the GDS?
if not - how can I get (as an OTA) this access?
As the mentioned potential duplicate shows, there is no direct way.
You can start booking tickets on the airline's site in multiple browser windows in parallel (keeping them all open and uncompleted), until no more tickets are shown available, but it is a bit tedious, and it might not work for all airlines, depending on how they handle the blocking.
