Hi NB
All my adjustable reamers are Imperial and (I've just checked) my smallest one is 9/32" to 5/16" (it's by Dormer)
I don't know if there are smaller Imperial ones available but my point is that (being adjustable) – these reamers also do "metric" holes too! The one mentioned above is good for 7.14mm to 7.94mm and was used on a 7.5mm 'hole' a few weeks ago.
None of mine were purchased new (so I've no idea how much they cost) and they generally get used if I don't have a 'standard' reamer to fit a particular need – especially metric sizes (just about all my standard reamers are Imperial too)
However – you don't mention why you need an 'adjustable' reamer? If it is a (single) particular sized hole you want to ream within this range – why not just make and use a D bit?
Regards,
IanT