The Diaclone line featured some unique campaign prize items. At the time Diaclone was available for regular retail in Japan, the market was very different from today. There were hardly any collectors so as you can imagine rare give away items such as the Diaclone campaign cars aren't easy to find these days. Luckily some items have surfaced and a few more recent Takara Transformer re-issues were based on these rare items. Most of the pictures on this page come from Himawari, owner of one of these rare items.
At one of the BotCon shows in Japan, BotCon Japan organizer Fumihiko Akiyama had a display of his amazing car robots collection. Amongst the regular (Diaclone) car robots were also two gold chromed Diaclone campaign cars. Fumihiko Akiyama is the lucky owner of the gold chromed Jazz and gold chromed Bluestreak. How many of these items exist is unknown, but there won't have been many made available and probably even less still exist. How these items were packaged is unknown, nor do I know if these items came with their accessories (although I assume that they did).
In the picture below you can see how you could become eligible to receive one of these items. The idea is that you bought one (or maybe more?) Diaclone item and send in part of the box. The scan below was part of a larger advert for Diaclone toys and was taken from a Japanese magazine.
Besides the gold Jazz and Bluestreak, other campaign items were a silver chromed Bluestreak and for the Micro Change line a gold chromed Browning. I don't know how you could become eligible for the Micro Change campaign items but I assume the process was similair. Below you can see images of the gold chromed Browning (picture taken from the Takara SF book) and the gold chromed Smokescreen which is owned by Himawari. The gold chromed Browning (I assume more than one exists) was sold at one of the US Botcons.
Another interesting item which was shown at the car robots display at BotCon Japan was the black Tracks that also inspired a later re-issue. It is still unknown how exactly this original black Tracks was available but the latest rumors point to Finland where it might have been sold. More...
Below you can see the re-issues based on some of the above rare items. The gold Jazz and silver Bluestreak were sold by the E-Hobby store in relative low quantity. The black Tracks below, even though it's a re-issue, was a campaign item by itself. It could be won by buying a book called "The Transformers: The Comic Trade Paperback" and sending in a form found inside. 300 were made available as a prize but more of these black Tracks' were produced and sold by various dealers (these are often referred to as backdoor items, or 'Lunchtime Specials').