Are the zips truely beyond rescue? You could try working a little Fabsil (it`s a waterproofer spray for tents, silicone based, so won`t hurt the outer if it gets on it by accident) onto the zip with a toothbrush and see if that gets it moving. You can get Fabsil in small spray on tins, so not too expensive.
we emailed outwell looking for a new 2 man bedroom for our indiana 8 and we got no reply i keep trying but nothing. if i find some where i'll get back to you.
Have you looked at the cost of replacing zips,it may be cheaper than a new inner,look on ebay you pick a bargin for £££s. Its end of season so prices are not so high.
If you live by a Dunelm Mill shop they sell zips by the meter, then you buy a pack of 'sliders'. I bought a heavy duty zip to put a toilet area in my tent between the two bedroom and it works great.
Putting in zips is easy so don't be put off by that. I am going to France on Friday for a couple of weeks, but if you want me to do the repair when I get back it won't be a problem. You don't live too far from me either so let me know ok.