After 8 weeks the DVLA have rejected my application for a V5 because I don't have dating evidence.  Can anybody tell me where I might get this please?  I'm told that evidence from a reliable source such as an owners club will be considered.  Could somebody point me in the right direction please?

I take it your talking about the (1977 XS 750 Special imported from Colorado) from your original post yes? If so you might try to contact Yamaha UK, Try here for phone numbers and such they are really helpful if you are stuck https://uk.yamaha.com/en/support/contacts/index.html  

Hope that helps and good luck.

Is there a label on the head stock? These give the month and year of manufacture.