If you are looking for models as it applies to a kit of parts that you assemble and not the ready made die cast example, there are white metal kits available of some of the various types or variants of the Austin Seven which I've seen advertised over the years. Other members on here can advise on what is currently available.
If you are looking for plastic models there is one that I know of but it is not strictly an Austin. This is the 1/24th scale 1929 BMW Dixi by Heller of France and now being sold under the Revell Germany label. While it is of the restored two seater in the BMW museum, it CAN be converted to a proper seven with some surgery and work. This is what I chose to do to make the AD van model I wanted:
[attachment=8319]
I have yet to make the replacement wheels for the horrid heavy items that come with the kit. Other possibilities are possible if you want to spend the time to do the conversions , otherwise this is the only Plastic kit I am aware of.
I hop this is of some help.
Cheers,
Stephen