Barchu Basrah

I daven in a standard Eastern European Ashkenaz schul. The custom is not to say a barchu basra, but we have Sefardim who daven with us. It is a very rare evening when there isn't a barchu after maariv. This is really bothersome as it is clearly not an Ashkenazi custom - but it is spreading. Anyone have sources related to the topic? Even for someone who misses barchu, unless you are going to recite all of keriyas Shema, it is not simple to randomly say barchu just because you missed it!