dear, what I know is what Xingzhu know ah!
AVAT and MRH offer max 1 gallon hydrosol, and AVAT is cheaper. 1gallon is around 60$, MRH is 102$. But MRH lavender hydrosol does not smell good based on Fannie's responds, and I don't like it either. Somebody love ATVT's lavender hydrosol, but I never tried.
I have did some research before:
http://www.provence-scents.biz/html/floral_water.htm
this one offer the best quality lavender from France Provence (I presumbly trust any lavender products orginated from this place, of cause with the right latin name and right distillation method).
http://www.essentialaura.com/lahy.html
this one is cheap.
I have tried ebay before.
another one
I have never used lavender hydrosol from these research link, so be cautious.