I agree, buy whenever you happen to see them available. In the past year or so, I have never seen Giovanni products at Marshalls at all, and only twice at TJ Maxx. There's no regularity or predictability with those kinds of stores.
Like the ladies said above, you have to buy it when you see it. The ones by me have it all the time (or at least everytime I go) and after looking at my personal collection, I had to stop myself from buying it. I have enough conditioner to last me a full year......
I bought 3 bottle which lasted me several months and bought it again last month. They are there it is just that they run out after a while come back a week or two later you will see them.