The Mackie produced Balmoral Bonnet comes in various headsizes, measurement being set buy the headband, but the actual bonnet part comes in a standard size, the options available are diced or plain headband, ribbons tie or loose.
Because I specifically went to Mackie's with a view to ensuring the best possible match to Jock's old bonnet, it was evident that the bonnet size had changed over the past 30 odd years, and they offered to make one up specially, so Jock's new bonnet is very bespoke.
But I am certain that as Mackie's hand produce every bonnet anything is possible, I can only ask.