Isn't the commonly available Avgas low lead (in comparison to conventional high lead Avgas) rather than unleaded?
There is supposed to be unleaded Avgas available but I have know idea how available or how much.
AVGAS 91/96 UL is increasingly available, typically 10 to 15p a litre cheaper than 100LL. The nearest airfields to me that stock it are Compton Abbas and Popham.
