Check the "somewhat new" Hydrangea Cityline Berlin in the link below but be wary of vendor claims. It may fit the bill but it is hard to know for sure unless someone has been able to grow it for about 10 years. That would help confirm the size at maturity.

Here is a link that might be useful: H. Mac. Berlin at Greenwood Nursery

I very recently purchased 2 Hydrangea Serrata "BLUEBIRD" PLANTS in an outof town nursery. I had forgotten my reading glasses and could not read the back of the tag. When home, I read that Bluebird is a dwarf, deciduous shrub with narrow, serrated green leaves that redden in the fall. Lacecap flowers are blue to reddish purple, with deep blue or purple inner rays. Use in containers or borders. Flowers in Summer. Without pruning: 4 - 6ft tall and wide. Likes part sun. These plants are a product of Canada - but no name of the grower was on the tag. Doesn't sound much like a DWARF does it?

pia is the best. it not only is 2-3 ft. tall but it reblooms and has large blooms.dj

Donna1952...I have grown many 'Bluebird' hydrangeas and they are in no way dwarf. Pretty, but not small. Tangerine

Agree, BlueBird being a 5x5' shrub in no way could be called dwarf.
I'm pretty much sure Berlin also will not fall into this cathegory. I had a barely rooted cutting of it last year and in a single growing season it become a 24" plant.
Of the all four Citiline series plants I have only Vienna and possibly Paris will be in a dwarf league, but jury is still out for at least couple of years.