Thomas Dalton wrote:
It would be a lot easier for the template designer, if the existing template (without modifying the wiki parser!) could link to an intermediary page called Special:Serialsource which could transclude text from a user-editable [[Wikipedia:Serial sources]].
Some way to access a post/get value in a page would do it, then you could just link to Wikipedia:Serial sources?issn=12345678. I can imagine hundreds of potential security issues with that, though, so it would have to be done very carefully. It could have lots of uses, though.
Special pages CAN read extra parameters. However, i'd advise the format Special:Serialsource/12345678 instead, as it can use internal wikilinks.