Sorry to hear that you did not great a positive response from Kent TRF
Taking any bike on green lanes on road tyres may be the reason behind the cautious response rather than the big bike. After all no-one wants to see you have an incident and as I am sure you are aware, on a motorcycle tyres are everything.
If you make it clear you have the option of off road tyres you will find a more positive response on the following TRF links/groups;
• The TRF Adventure bike riders FB site – open to non TRF members to join.
https://www.facebook.com/groups/advbiketrailriding/
• The TRF forum again will be open to non TRF members to join.
www.trf.org.uk/forum
• For the last 30 if not 40 years the TRF has run the Coast to Coast which is again – big bike friendly groups,, you will need those second wheels though.
http://www.trf.org.uk/the-yorkshire-coast-to-coast/
• Of this month’s major TRF events, the Hereford Hospice run is unlikely to be suitable but the TRF Moorland event might be if you check with the organisers.
other TRF events are listed here
https://www.facebook.com/pg/TrailRidersFellowship/events/
This year’s TRF supported Byway tours for the wounded set off from Kent this year so I know there is plenty to do on a larger bike. You will always get a wider opinion by turning up a group meeting , details are here.
http://www.trf.org.uk/find-your-regional-group/
Rick Kemp the TRF’s editor an ex TBM is based in Broadstairs and the Sussex TRF guys ride Kent as well- so please contact them if you don’t get what you need from Kent TRF.
You mentioned the Silk Road – nearer to you would have the Pilgrims Way which would seem to be an natural first step nearer to home.
http://rustracing.com/the-pilgrims-way---part-1.html
The other side of the M25 from you , Herts TRF run regular big bike only days and many TRF ride leaders will have ridden the route you are planning to do.
Here is a photo from this summer of the new to TRF Dolan Family, Mum on here GS with Dad & small child on their GSA.
This was taken in NW London on a Herts TRF beginners run.
https://photos.google.com/album/AF1QipPXz5imAUmjNuuWJgV65R-DAj69rsOQ_MK5rYPs
Likewise here is a rider from the Herts TRF all bike beginners ride last weekend on his Triumph 800 suitably shod.
https://www.facebook.com/HertsTRF/videos/1686441684722790/
Herts TRF will take out beginners on road tyres when the conditions allow – normally mid-summer when dry, or on a Salisbury Plain or Thetford forest run. See here
http://www.trf.org.uk/big-bike-party/
There would appear to be a suitable TRF green road ride for any big bike on road tyres led by professionals here.
https://www.facebook.com/events/256637554845473 If you call Marianne (details in the link) I am sure she will help you further.
Finally if the TRF isn’t working out for you and you simply want to find some green roads yourself- take a look at the TRF supported TET for a routes across the England & Wales which or Trailwise in your local area.
http://www.trf.org.uk/the-trans-euro-trail/ Key people at the top behind this such as John Ross & Greg Villalobos and Brian Elland are all TRF officers / volunteers. You will definitely need off road tyres for this run. The route has just been extended in the South to run to Dover, Kent
Hope you find this helpful and please let us know how you get on.
Regards
Mario