The open data portal only enables LIDAR data to be downloaded in 5km x 5km tiles. The portal is unable to deal with large data requests.
It's now possible to download several tiles at the same time (see here), but this can only be done for relatively small areas.
There's no option of bulk download for the whole country or for a large area. This would need to be supplied offline.
To order an offline supply of LIDAR data, make a request using the "Submit Feedback/Report an issue" option on this forum. Please advise what data and resolution you require.