Q] Where can I watch this?
A] Official releases of Scramble City: Mobilization outside Japan are somewhat rare. The episode was included on Sony BMG's The Transformers: The Movie 20th Anniversary Special Edition DVD, but famously, it does not include any audio or subtitles. This was apparently because of problems dealing with Toei (who animated the episode). Instead, this version includes commentary from Rik Alvarez and Alex Weiner.
In the UK, the episode was included on Metrodome's The Transformers: The Movie Ultimate Edition. The version used was a fansubbed bootleg, only due to a poor standards conversion from NTSC to PAL led to the episode having a green tint, making it look horrible. The subtitles cannot be turned off and the video quality is poor. It does, at least, have the original audio, and there is also a commentary track from Chris McFeely.
Madman Entertainment released a new special edition DVD in 2007 for The Transformers: The Movie, and Scramble City: Mobilization is a bonus feature on it. It includes the Japanese audio, I'm not sure if it has English subtitles.
Of course if you don't want to own a physical copy, you can usually find the episode on Youtube. There are fansubs and fandubs available.
Q] Doesn't this episode start with clips from previous Transformers episodes?
It does, specifically, it uses clips from "More than Meets the Eye Part 1" ("The Road to Earth" in Japan) and "The Master Builders" ("Master Builder" in Japan). The clips show the Transformers arriving on Earth, along with a few clips of Devastor being a menace. This clips take up around 7 minutes. The reason I haven't included the clips on my overview is because the version I had to take images from didn't include it.
Q] Wasn't there another episode of Scramble City, but with toys?
A] There is another episode called just "Scramble City", which was also released in 1986. The episode is actually a re-telling of Scramble City:
Mobilization, but mostly uses the actual toys to tell the story via stop-motion. Some clips from actual Transformers episodes are also used. The stop-motion version of the episode also has Galvatron appear in it, who Megatron orders around -even though they are the same character! This error was because of a miscommunication between Hasbro (who dealt with Transformers in America) and Takara (who dealt with Transformers in Japan).
For more information about this episode, visit the TF Wiki.
Q] If Dinosaurer is built in this episode, then what happens in the Japanese dub of "Five Face of Darkness, Part 4"?
In the American version of Five Face of Darkness, Part 4, Trypticon (Dinosaurer in Japan) is created in a city by the Constructicons (Buildrons in Japan). For the Japanese dub of the episode, the dialogue was changed so that the Buildrons were "rebuilding" Dinosaurer. This hints that Dinosaurer lost in his first, unseen battle with Metroflex, and was heavily damaged.