The key info is not that standalone LR6 is still available from some sites. The key info is that standalone LR6 is a discontinued product. If you are starting out from scratch and not upgrading an existing LR installation, consider very carefully if you want to build a catalog, organise your photo and have all your edits on LR6 standalone. You may need to go for the subscription model in the future to keep abreast with the new features.
As for me, I have been a user since LR4 and am using LR6 standalone. I am currently looking for an alternative as I do not want to use a subscription based s/w app.