Is there an extender for the Canon TS 24mm? I heard it is possible to make it a 45mm but I can't find much information on the web.
Both Canon 1.4x and 2x extenders work - more information here (search within the page for extender). Additionally, fitting this on a 1.6x crop-sensor body will give an equivalent of 38.4mm focal length. This route would avoid the incorrect aperture reporting issues, and potentially offer better image quality than when using an extender - if you happen to have access to a crop-sensor body of course.
Canon teleconverters won't fit because they have a protruding front element that needs a corresponding recess in the host lens, which only the Canon L-series teles have, but third-party ones from Tamron and others should fit. Not Sigmas, they have similar design to the Canons. Optical quality is another matter, it is usually desireable to stop down a bit to mask the quality loss with a teleconverter installed. And frankly I have no idea if this will work at all if you tilt or shift the lens... Actually, I have the Canon 24mm tilt-shift at home (mkI, but it should make no difference), and a 1.4x converter, so I might just try this out for laughs.
Anyway, assuming that it works, a 1.4x converter would make the 24mm into a 34mm, a 2x will make it a 48mm. With corresponding loss of one or two f-stops, respectively. The 24mm f/3.5 will become a 34mm f/5, or a 48mm f/6.3, or something like that, anyway. And as said it is usual to stop down a bit to regain a bit of the lost sharpness and contrast with a teleconverter in place.