This is probably a limitation of the UI rather than the unit directly - I've never used this SA but it certainly looks like the UI is just truncating the buffer - Install whatever the appropriate communication software is (NI VISA, Keysight IO Libraries, PyVISA etc) and then write a small program to send the command and read back the data - You'll probably end up with several hundred values that will be distributed from the start and stop frequencies of the sweep - For example, my HP 8563E returns 601 values so I would simply calculate the frequency based on start, stop, divided by 601.
Not sure if this helps very much but maybe it'll help you find the right answer.
TonyG