The LTDR data can now be obtained from LAADS, via a HTTPS protocol. The URL from which data can be obtained looks like this:
AS = archive set, which would be 464 for Version 4 data and 465 for Version 5 data.
ESDT = N11_AVH02C1 for L1B, N07_AVH09C1 for surface reflectance, N09_AVH13C1 for NDVI etc.
Note: the NXX represents the NOAA AVHRR sensor ID.
The following link goes into detail regarding how to get the data:
To summarize: If you are not already a registered user of LAADS, create a profile with Earthdata (https://urs.earthdata.nasa.gov/profile). Connect to LAADS archive and generate App keys (under the menu profile). App keys are tokens that identify you, and they get put into HTTP GET commands when downloading the data. The above website explains all that in more detail. That website also gives examples of scripts (in Perl, bash, or Python) that can be used to download data.
Here are additional perl and python scripts that you could use to download the LTDR data