Besides lymph nodes, where would you expect to find proliferating (dividing) b cells?

We can expect to find dividing and maturing B cells, aside from the lymph nodes, is in the spleen. The spleen is one of the major lymphoid tissues (i. e. lymph nodes, thymus, mucosa associated lymphoid tissue, etc) where lymphoid cells proliferate. The major cell from the lymphoid lineage that proliferates in the spleen are the B cells.