Is there a mod that allows me to make the topic link into an external link to another site?
there is one for boards (redirection mod)
but not one for topics at the moment.
What would I have to do to make one?
You could ask in the Mod Requests forum. (or ask this topic to be moved by the powers-that-be)
But I know that someone had asked in the past (but never got made).
If you are willing to pay for it, there maybe someone who would make it for you by posting a paid or free request in the help wanted section.
If you would like the topic to be moved, as per karlbenson's advice, then I'll do my best impression of "powers-that-be" and move it for you...please post to make your wishes known.
Can you please move it.