Not sure if anyone knows about this but there's a guy operating in Pitmedden who does motorcycle tyres. He has a small unit just opposite the Chinese chipper and can supply and fit tyres.
I don't think he has a great range in stock but if you give him a ring he'll sort you out.
I got this from Wildcat Cruisers website but I have used him as well. He works in the evening as I think he has a day job somewhere else which means he's not there in the day.
Craigston Tyres of Pitmeddon - For a great deal call Neil on 07758 779989
Phil