The first Sonic Adventure on the Dreamcast had a Black Market just like the sequel. The archived version of the original website still has the pages and CGI scripts for it, as well as VMU files, which we’re going to look at today.
I didn’t access the Black Market back when it was online, but I’ve heard that the US version never worked because of some bug. The messages from Chao Doctor all the way to January 2000 mention that the Black Market was about to launch, and the comments in the CGI script used on the website suggest it was indeed broken at the time of archival:
The Japanese version was functional though, and it was possible to download several jewel Chao. The Ruby and Emerald Chao didn’t have any emblem requirement. It looks like they were given out “for free” to celebrate the Dreamcast’s US and EU launch anniversaries. However, according to this page, the Emerald Chao was released during an event “Magical Garden: Yume no (‘Dream’) Dreamcast Festival” that took place on March 27, 1999. I can’t find any other information on the event so I’ll have to leave it there for now.
The Amethyst Chao was unlocked when you had 100 emblems. The Sapphire Chao isn’t referenced in the pages or scripts but its VMU data exists. Apparently the US version was going to add a new “NiGHTS” Chao that would also cost 100 emblems. Although the NiGHTS Chao is referred to as “very special Chao”, it’s actually a regular Fly type Chao with animal parts rather than a unique character Chao, which SA1 doesn’t support anyway.
Chao downloads are stored in 8-block VMS files, and Japanese files have a different header although the data is compatible between all versions. There’s a script on the website (likely used for Chao daycare) to generate Chao VMS files, and it alternates between Japanese and US headers, which are stored as binary data on the website. The header is set up like a VMU game header, similar to Chao Adventure. Here are all the files found in the site’s archive:
|NiGHTS Chao (US only?)