The workhorse for gathering the information will be the following command.
myvlans = meraki.getvlans(apikey, networkid, suppressprint=False)
You'll want it to loop through the networks you have and then loop through the VLANs that this command pulls. The reservations you have set are based on MAC rather than IP, which can introduce some interesting issues depending on what you are doing with this data.
Why Meraki (who allow you to upload reservations via CSV file) don't allow you to download existing reservations via a CSV file is beyond me.
Good luck!