Please load index file rdrindex.tab from https://planetarydata.jpl.nasa.gov/img/data/mer/mer2mw_0xxx/index/rdrindex.tab
File will be processed to extract data about available 3d files per each site/drive (.PFB, .VST, .HT).
Use filseAvailability["sitexxxx"][driveNumber] to get all available files.
Use (filesAvailability["sitexxxx"][driveNumber] || []).filter(file => file.filename.endsWith(".YYY"); to get all available files with extension "YYY".