Unfortunately, beta sites do not get custom migration targets.
If you happen upon a question that you think would fare better on a different site, feel free to flag for moderation attention and ask for it to be migrated. Do keep in mind, though, that only high-quality off-topic questions should be migrated. If a question is on-topic on Politics, or if it's ...
Politics Stack Exchange is still in beta. Beta sites do not allow to set migration target sites other than their own meta.
But moderators can migrate a question to any stack exchange site they want nevertheless. So when you find a question which is off-topic here but would be on-topic on a different stack exchange site, flag it for "in need of moderator ...
This Q has been raised numerous times on Meta.SE: one, two, three, and the consensus is that, migrating old Q's is generally a bad idea, its downsides overweight its benefit.
Just VTC, and if a new SE site has emerged since then, nothing prevents you from asking it there, providing the link to the existing Q here.
You would have to have a community manager migrate it at this point. Site mods have a 60 day window, same as close-migrate votes.
You'd need a super compelling reason to get it moved at this point. Just leave it.
See Migrate to *any* site?
user4012 mentioned this in a comment, but it was strong enough that I think it's the actual answer:
SE migration policy prevents this from being a viable option. Questions should not be migrated just because they are a better fit for another site. Questions should be migrated when they are off-topic on the current site.
In addition to that, it looks like ...