Yes, the Registry used to be the place to advertise plugins and scripts but now it is in read-only mode (spamming went out of control).
Then there is GimpScripts.com but it hasn't got the audience of the registry. Otherwise you can advertise on the forums and mailing lists, but it is best when the script is an adequate answer to a question.
On the other hand you should wonder if you aren't reinventing the wheel because the description you give "prevent color bleeding on textures when using textures with an alpha channel" looks lot like using the alpha-lock.
Then there is GimpScripts.com but it hasn't got the audience of the registry. Otherwise you can advertise on the forums and mailing lists, but it is best when the script is an adequate answer to a question.
On the other hand you should wonder if you aren't reinventing the wheel because the description you give "prevent color bleeding on textures when using textures with an alpha channel" looks lot like using the alpha-lock.