The Seviper in the set described earlier is from the same magazine issue, but on the third page (all the pages I posted should be from the same magazine issue), so it would be (Pokemon Advanced Generation Ginpika Medal (Page 3) - Shogakukan Yōchien Magazine - July 2004 Issue). We know this, because the front of the magazine advertises 100 medals, and all three pages together would be 100 medals. (It also states page 3).
As for your other Seviper:
Pokemon Ginpika Medal 395 (Part 3) - Shogakukan Yōchien Magazine - October 2006 Issue
Edit 2: It seems that these were split up across multiple issues: Part 2 being September 2006, and Part 3 being October 2006. I wasn’t able to conclusively find a date for Part 1, but I would guess it to be August 2006.
Edit 3: Found all three parts–each page was released in August (Part 1), September (Part 2), and October (Part 3) issues respectively.
Here are all the relevant pictures I was able to find:
Your Seviper can be found on Page 3 in the picture above (middle bottom in this full picture).
It seems to also have come with this insert:
Edit: I found pictures of the magazine:
Edit 2: Included ones for September. The one for September shows that it only includes part 2:
Edit 3: found all the parts:
August 2006 Issue (Part 1)
September 2006 Issue (Part 2)
October 2006 Issue (Part 3)
The top right here on the page in the middle states Heisei 18 (2006), 9th month (September), and that it is from the Yōchien magazine, which gives us the issue. (It is the small black text above the red rectangle, as well as the purple rectangle in the top right, so it can be hard to read).
Edit: perhaps below is the print date, not the release date; the actual magazine images are for October 2006.
Edit 2: I see what has happened here: each one of these pages was released in a different issue. See above.
