ok it was an LA sleeve and the cost was retailed out at about $300, not sure what it was direct probly half that. LAst time i looked it was these guys or NOS only, didnt turn up any other makers last time.
The part number in the book is YA 658SL ,
i think this is the web site just send them an email asking what they can do one for trade etc.
http://www.lasleeve.com/master.html if you go to a serco reseller they will have this in their catalouge as it also cover the wisco pistong for it etc.
Although its for the 73-74 MX 250 it also Funnily enough iafter the product code the numbers 1976-79E
im wondering if the 76-79 YZ E uses the same sleeves ? you might find one of those on the shelf in Au already ? up to you dude above is all the infor you need to get going :O)
see how you go.