In what form are you looking for it? I have seen Chamomile Lavendar tea at many health food stores under OK supervision, plain lavendar is readily available but i have never seen it with hashgacha
if you are in the NY area there is a small store called ‘flower power’ that sells dried herbs that definitely would lavendar. this kind of item may not need hashgacha (as long as its not from EY) tho it prob needs to be checked well for tolaim. hope this helps.