John normally sells them, but is out of stock at the moment,
I'm sure if you contact him he will be able to give you an e.t.a.
https://www.tytrials.com/trailandtrialsuk/prod_691227-1-2-Rear-Spoke-Set-TY80.html
Hi,
If you would like to PM me your direct e mail address, I can send you a PDF file which will tell you which spring you require based on your weight.