Dennis, the TJ16 is currently in stock (see link below). The out of stock item you are asking about is an optional installation kit. An alternative to the installation kit is the TJ16 "Inline Bypass" you'll see as an accessory on the TJ16 product page.
https://www.circupool.com/CircuPool%C2%AE-TJ-16-Typhoon-Pre-Filter_p_74.html