I rang Toyota when I found the sensor missing and asked for a price........................................ $600 - $700 with an 8 week lead time
Also asked for a cross reference to see if they used the same sensor on any other engines but no luck
Toymotor spares in Wordsworth street has a box of Map sensors, none for the 1ZJ, which you could try, maybe find one that will get you by until a real one turns up.
How did the new exhaust turn out ?