It would have to be from another company, like ATI or such. From what I hear from other forums HP is having a hell of a time keeping up with demand, not to mention they just put out their .45 carbine and the new TS stocks. Also there's not likely a large enough market to justify them designing, testing, and setting up the tooling to make another carbine design/stock. The US traditionally hasn't been a very fertile ground for bullpup sales.
As a sidenote, they're already pretty short and handy carbines and have a good balance to them. I'm not sure how well they'd balance in a bullpup format. Neat idea though.