To avoid looking like a pushy salesman, I'd like to make it clear now that I work for Clarks who are a forestry equipment supplier. I don't wish to use this place as an advertising board, nor have I any intention of shoving products down peoples throats - please could someone let me know if there are any issues with me posting here (I promise only to add to discussions that I feel I may be of some help to!)
Right, now that's out of the way... there are a couple of manufacturers of chainsaw trousers that might just have something suitable for you James - they're SIP and Stretch Air.
Stretch Air are right up at the top end of the market (in terms of both quality and, unfortunately, price!) and firmly aimed at professional chainsaw users and Arborists. SIP meanwhile have a huge range and are a bit lower priced.
Stretch Air chainsaw trousers have the option of an additional 7cm leg length - see here for an example:
http://www.clark-engineering.com/forestry-equipment-shop/detail/119/118/stretch-air-full-stretch-chainsaw-trousers-type-c
This would mean that you could simply order the size that fits your waist and add the extra 7cm to the legs. Be warned, Stretch Airs are excellent, but they're not cheap!
The other option, which I've not yet got added to our website (but I'm working on it) is the SIP Traditional Tall - see here:
http://www.workware.co.uk/by-brand/sip-protection/chainsaw-trousers/1sp3-traditional-tall-chainsaw-trousers-a-gree/orange.html
These would be roughly around half the price of the Stretch Air's.
Hope this helps to at least give you some hope that there may be something available for you?
If I can be of any more help, please let me know.
Cheers
James