As reported on GoGreenMachine, ASDA has the
Secret Sewer playset listed and it looks available for purchase.
I took the Oct 1st announcement with a pinch of salt. It isn't like Playmates were doing a Force Friday event around this line or anything. If stores get something in, they'll fill the shelves and it is now the run-up to Christmas.
Besides which, previous TMNT releases have surfaced early many times before.