How to install new Netflix on old iPad?
What version of Netflix is stored with your iTunes Library on your Mac/PC? You could check this to see whether you still have the old version:


If so: you can select and sync the Netflix app from your iTunes library to your iPad.
If not, and you have a Mac: Your Time Machine backup should have backups of all the apps previously downloaded/synced with your iPad. These will be located within your iTunes Library. So you could go back far enough to find a version of the Netflix app that will work with your iPad and restore that version to your iTunes Library. Then select and sync that version to your iPad from within iTunes.
If not, and you have a PC: Assuming you have past backups of your iTunes Library, you can do the same as above (i.e. copy back a version of the Netflix app that will work with your iPad to your iTunes Library. Then select and sync that version to your iPad from within iTunes.