I'm guessing in the timespan between the ep where the Technodrome was destroyed and the final one, Shredder and krang moved on with their lives until transported by Dregg in the final season. That or they were kicked out by those aliens who were in the last ep threw them out.
--Previous Message-- : In the final episode, I remember that : the technodrome was stuck in : dimension-x and krang and shreddar : were stuck on earth. Krang's rock : soldiers got the technodrome free : from the black hole that it was : stuck in. Later, the turtles got : to the technodrome and destroyed : the engines. A giant plant monster : grabbbed the technodrome and krang : said,"I rue the day I met : those blasted turtles!". The : technodrome got pulled upside down : and landed on the ground, eye : first. That was the last episode I : had ever seen made. Never once did : I see the technodrome destroyed. : Knowing shreddar and krang, they : could no doubt find a way to : repair the engines and create a : portal to earth large enough to : get the technodrome through. I : remember that season well because : in every episode the sky was red : and shreddar's voice was : different. The show wasn't under : Dublin instead of swenson. And did : anybody remember the new episodes : they had on fox a few years ago. : There were ones with shreddar's : mother and the energy collector : that krang stole from another : dimension that was like $19.95? :