We have a Utah 6 which is identical in scale to the Dakota (I think just the colour and SIG are the differences). There was a thread a few months ago discussing how to get an extension for it: here
Hope you find what you're after.
------------- Mostly Mrs Mickeyboyc
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Have answered on your other thread, we have a brand new extension for the Dakota 6, never been used. We will be selling it when we get back from holiday end of the week, also have carpet, footprint and Dakota 6 tent, used for 4 nights only.