John Deere 4052R Cab,, Deere 855D UTV, Z920A Zero Turn Mower and assorted implements
If you were in the US, I'd suggest a salvage yard.
However, your use of the word "bonnet" indicates you're in the UK...so, maybe a local yard in the UK or Europe?
Pretty old Kubota...good luck on finding what you need...
The bonnet is made in three parts. along with the grill everything could be shipped flat. If you could find a yard willing to break it down for you. That Kubota is old but well built. If anything else rusts out or falls off mine will quickly become a Boomer look alike. The old ford sheet metal and fenders are pretty close.